General Question

trypaw's avatar

What is this knocking/popping noise from inside my car?

Asked by trypaw (327 points ) October 19th, 2012

Hello,
So last night I noticed a knocking/popping coming from my car when it is in “park” or “neutral” the noise is like a knock,knock,knock continually and I can feel it thump/pop through my brake pedal )pressed or non pressed). It doesn’t happen when I’m in drive or at stoplights or anything. Only when I’m in park or neutral and after a couple seconds I hear the knocking. I cannot hear it outside the car or when I open the hood. I can only hear it inside the car, sounds like its coming from the front of the car. Any idea of what this could be? I’m open to all suggestions I drive a long way to work and need my car for my job. I like to find out what problems are as soon as I suspect one.

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39 Answers

tedd's avatar

Dear I really think it’s time you buy a new car, lol.

Anyways, this could be a lot of things. My immediate concerns are either your engine is knocking, or your motor mounts are going bad.

If the engine is knocking, this means it doesn’t have enough oil. The “knocking” sound is the pistons hitting on the metal everytime they go up and down. It would probably be getting worse (louder and more frequent) when you were accelerating though. So the good news is it’s probably not that. Either way though it never hurts to check your oil (especially with your car). Keep an eye out for any shiny objects in it if you can (those are metal shards).

If your motor mounts are going out, you would notice the car kind of “pulling” itself from the ground on one side (not both). The motor mounts literally mount the motor to the frame of the car, when they are going bad they start allowing the engine to twist as it’s momentum would like it to do. This also though would present itself more powerfully while accelerating (in my experience at least). If you want that checked you’ll probably have to ask someone knowledgeable on cars to check it for you.

The only other kind of major concern is one of the belts (which thinking about it is probably the most likely culprit). A belt could be slipping or knocking when the car is colder (aka if it goes away after you’ve been driving this is a good symptom of a belt). Easiest way to check is to turn the car on and pop the hood, look/listen for noises or what have you.

Honestly without more symptoms or information it’s kind of hard to tell, but there’s some things to start worrying about, lol.

But like I said… new car time… lol

Adirondackwannabe's avatar

The thumping is coming through the brake pedal only? See if you can feel it through the gas pedal, and see if it changes if you increase the rpms of the engine.

trypaw's avatar

@tedd thanks.. And yeah I know. But anyways the problem actually starts when the car is all warmed up like. 20 mins of driving. It doesn’t happen at all when its cold. And the vehicle doesn’t do anything else weird. Steers fine drives fine, no power loss, acceleration is fine. ugh.. I just don’t know.. I just really need to be able to get to work. lol that’s all I care about. I don’t need the thing exploding on me. haha

trypaw's avatar

@Adirondackwannabe yes only through he brake pedal when in park. I don’t feel it as I’m stopping at all. The gas pedal doesn’t do it at all. I will try the rpm’s.

Adirondackwannabe's avatar

I’m thinking bad brake cylinder, which might also explain the other things you were hearing. Or the other simple possibility would be the brakelines weren’t bled properly.

CWOTUS's avatar

Please ignore most of the uninformed first response.

If the pistons were “hitting metal” as they travel, they might do that once or twice before the engine simply freezes or cracks into pieces. The pistons are not hitting anything if the engine is still running.

However, the concern about motor mounts is valid. A mechanic could probably tell you that (probably at no cost to you) in a couple of minutes. Fixing them could be more problematic, as the engine has to be actually lifted (at least partway) from the vehicle to replace them. But they aren’t expensive in themselves, so it’s the labor charge that would cost for their replacement.

It’s the fact that you can feel it through the pedal (and when the car is stationary), that makes me think “motor mounts” as most likely.

Another thing that makes noise, but not vibration, is loose tappets and/or valve lifters. These can create a sort of “chattering” sound, but you’d be very unlikely to feel any vibration, and you’d normally only hear them when the engine was under load or when the hood is lifted.

trypaw's avatar

Also it’s very quiet it that matters and I really love my car it’s the only thing I have left from my parents and its very important to me.

trypaw's avatar

If it were the mounts wouldn’t it produce the noise when I’m diving or at a light? It’s only when the car Is parked and not moving otherwise to sounds nothing weird at all.

Adirondackwannabe's avatar

I’m baffled. It stops and accelerates fine? No noises like the knocking? I don’t think it’s the motor mounts. The car hasn’t been in an accident has it?

Tropical_Willie's avatar

Does it make the noise when it it out of gear or in “park” ?

Also is it an automatic transmission?

trypaw's avatar

No accidents. And it makes the sound in park or neutral when the car isn’t moving. It’s auto trans.

trypaw's avatar

And no, no noise or knocking when driving or accelerating. No shaking at high speeds nothin.

Tropical_Willie's avatar

When you get out of car while it is running, walk around the vehicle and see if you can ( with your eyes closed ) point to the location of the noise.

trypaw's avatar

I tried to find it outside my car but I can’t hear it or feel it. I can only faintly hear it inside the car.

trypaw's avatar

Also thank you everyone for your help it really means a lot to me. I just hope we can figure something out.

tedd's avatar

@CWOTUS lol… right buddy. I’m unfortunately very familiar with what a knocking engine is, and have been pretty well educated on the area by my family who design cars for a living. Anyways like I pointed out, I don’t suspect that is the issue.

@trypaw Did you listen under the hood from outside the car? If the noise isn’t coming from there then you are probably eliminating most of the problems we’ve listed here. Could possibly even be something as stupid as something to do with the heating/cooling system. I’ve had that happen before, where something breaks and suddenly it makes a weird noise.

trypaw's avatar

Yes I listened under the hood. I cannot hear anything but my normal engine sounds. This sound is really getting on my nerves just cause I want to know what it is, if its nothing I could live with it but until I know that lol. I’m going to keep on hunting.

Tropical_Willie's avatar

Does it come from UNDER the car like a catalytic converter, bouncing and belching.

trypaw's avatar

I can’t tell I just know I hear it sitting in my drivers seat sounds like its coming from forward of where I’m sitting and makes my brake pedal knock with the sound. My boyfriend has a bad catalytic converter and it sounds completely different.

Tropical_Willie's avatar

It maybe that an exhaust pipe has a broken mount or clamp. That is the reason I asked about if the sound was under the car. After the car heats up the metal moves around and expands.

jerv's avatar

@CWOTUS You’ve never seen a Toyota 4A-LC then. I saw one run for almost a month like that before it blew. However, I agree that it’s likely a valvetrain issue, especially as it seems temperature-dependent. The sound that Toyota made could be heard three blocks away, and did it hot or cold; very unlike what the OP describes.

CWOTUS's avatar

I cannot discount your automotive experience and knowledge, @jerv, but I stand by my assertion that pistons don’t “hit things” for very long without causing grave and usually irreparable damage to engines. I agree that lots of things related to engine revs can cause loud noise and vibration (and a piston interference problem would be loud, continuous and harsh), including worn crankshafts or crankshaft bushings, worn piston rings, cracked cylinders, low engine oil and even exhaust manifold cracks that can create “banging” noises. But a piston “hitting something” happens once, twice, three times, maybe up to a hundred or more (and if the interference was “slight”, then maybe 100 miles), and then the engine is toast and never runs again.

The OP doesn’t have a piston interference problem.

jerv's avatar

@CWOTUS Correct; they usually don’t. It’s rare for that sort of thing to last for more than a few seconds (if you’re lucky) without something catastrophic happening. I’m just saying that I’ve seen some weird things, and the 4A-LC is one of them.

Adirondackwannabe's avatar

I can’t figure out why it’s coming through the brake pedal. I wouldn’t worry too much about some knocks, but the brake pedal is really bothering me.

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trypaw's avatar

Yeah and thing is just had my rotors and brake pads replaced not too long ago and now I wonder if this sound is related to the brake job? Maybe they forgot to do something?

Adirondackwannabe's avatar

It’s in park or neutral and it doesn’t happen at stoplights. I’m changing my idea. It’s not something related to the brakes maybe. But why is it coming through the brake pedal?

trypaw's avatar

So you don’t think it’s related to the brakes?

Adirondackwannabe's avatar

I honestly don’t know. I would think it would show up when your braking. The car would pull one way or the other or not stop well. Have you checked the brake fluid level?

trypaw's avatar

Yeah it doesn’t pull and the fluid is fine.

Adirondackwannabe's avatar

I went looking and came across two possible answers. One said the vibration dampner might be acting up. I didn’t even know that existed. The other was the EGR and pollution control stuff at idle. The pollution control stuff at idle might come back through the brake pedal but not the gas pedal because the throttle linkage damps it out. Maybe see if it does it if you rev the engine a little in park.

trypaw's avatar

Ok I will try that tomorrow thank you so much :)

Jenniehowell's avatar

My guess is the motor mounts

Jenniehowell's avatar

I’d also recommend listening to & calling in to talk to the guys from the Car Talk(NPR)-p36/ radio show. They are way knowledgeable and helpful and they are pretty funny as well. I never would have thought a radio show about cars to be as entertaining and non boring as they manage to make it & they are way helpful to all their callers.

trypaw's avatar

@Jenniehowell I don’t think its the mounts because the problem is only when my car isn’t moving and only in park. Otherwise I have no abnormal sounds driving, but yes! I have heard of car talk! I will give them a try if I’m able, thank you!

trypaw's avatar

Read somewhere it could be my ABS prematurely cycling? What do you guys think?
PREMATURE ABS CYCLING
Symptoms of premature ABS cycling include: clicking sounds from the solenoid valves; pump/motor running; and pulsations in the brake pedal. Premature ABS cycling can occur at any braking rate of the vehicle and on any type of road surface. Neither the red BRAKE warning indicator lamp, nor the amber ABS warning indicator lamp, illuminate and no fault codes are stored in the CAB.

Premature ABS cycling is a condition that needs to be correctly assessed when diagnosing problems with the antilock brake system. It may be necessary to use a DRBIII scan tool to detect and verify premature ABS cycling.

Check the common causes when diagnosing premature ABS cycling: damaged tone wheels; incorrect tone wheels; damaged steering knuckle wheel speed sensor mounting bosses; loose wheel speed sensor mounting bolts; excessive tone wheel runout; or an excessively large tone wheel-to-wheel speed sensor air gap. Give special attention to these components when diagnosing a vehicle exhibiting premature ABS cycling.

After diagnosing the defective component, repair or replace it as required. When the component repair or replacement is completed, test drive the vehicle to verify that premature ABS cycling has been corrected.

—Not sure if it completely matches my problem or not?

Adirondackwannabe's avatar

@trypaw That makes more sense than anything else I’ve come up with. The brake pedal thing was what baffled me.

Jenniehowell's avatar

The other thing you can do is go to the local parts store and spend 20 bucks on one of those books for your specific car. Once you’ve got it narrowed down to a few choices like you’ve done here on this forum you can then read about those things in the book. They have a pretty good description of the possibilities in each section so you can get a better idea & even fix it yourself if you’re interested in doing so & able to do so.

If you do find that it is the ABS… I may actually take it to a different place for a diagnosis just out of curiosity to see whether they can tell you anything was messed with – it’s kinda suspicious that you just had brake work done and now you’ve got another issue in that area. Mechanics aren’t immune to securing themselves more business in that manner.

gm_pansa1's avatar

…....it’s your car telling you “there’s no place like home.” :)

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