What do you think is causing this internet problem?

Just about every day for the past couple of weeks, the internet connection has been down for up to eight hours. Otherwise, it works fine.

Some details:
1.) It’s a one year old desktop connected directly to a modem.
2.) The modem has been changed out twice since this started.
3.) All wires are new.
4.) I’ve tried using a different cable outlet…same problem with both.
5.) According to the internet provider, no one else in the area is experiencing connectivity problems.
6.) Internet connection slowly grinds to a halt in ~15 minutes about mid-morning and slowly reconnects late afternoon or early evening. Some days, there is no interruption.

The next step is to have a technician come out and check the wiring in the house. I’m just curious what could possibly cause this when it works well at times and doesn’t at others. Any ideas?