My guess would be maybe a registry problem of some sort or maybe malware of some kind.
Have you tried scanning for both?

Another idea, probably stupid but worth thinking about, could you have a...

Have you tried stress testing?

If it has a program that runs it, scheduling it to startup might help. If so, you can try this:

How to Add Programs, Files, and Folders to System Startup in Windows

Another idea I can think of...

Sounds like a real mystery... My first guess would be maybe a problem with the speakers, i.e. maybe a notification sound of some sort built inside them.

What kind are they?

Had the same problem, drove me nuts.
After you try all the usual stuff try updating BOTH your Bluetooth and Wifi drivers, apparently it's common that they correlate with each other.

If you can't...