What could be causing this ammonia smell?

Okay, so we have a big problem. Our entire house reeks of ammonia.
Now, at first we assumed one of our cats sprayed. They have never done this before, but we had a terrible storm on Thursday, which knocked our power out for almost 48 hours. The heat and humidity have been 90 degrees (F), and it’s so humid. Unbearable.
So, yeah, I assumed it was cat pee so we scrubbed the kitty little boxes and the tray and sprayed this “Ewww!” enzyme product which just freshened the air it seems.
We borrowed a strong UV light, and looked all over the house for the source of the pee.
We can’t find it anywhere. Also, the smell isn’t in one spot, it seems to be all over the house..which doesn’t make much sense. We checked the duct work to see if he might have peed on it but he didn’t.
What else could it be if not cat urine?! Could the humidity and water damage (yes, our basement had some minor damage..) have brought it up from past owners?
I’m at a loss. It smells so bad when you first walk in and I’m concerned about breathing in whatever it could be, since it doesn’t seem to be cat urine. Even having the a/c running 24/7 doesn’t help!

Any advice?