I think I may have a bad ground somewhere but when I touch any metal part of the PC, I get a buzzing hum from the sub woofer. The 2.1 speaker set doesn't use grounds from AC and to the best of my knowledge, no ground loop outside the subwoofer. I checked with my ohm meter on the cable from PC to system and each of the set of cables going to 2 other speakers, no cross short or anything unusual. The power source is a 12v brick that sits in the outlet, only 12v DC goes out to the speakers. I checked with AC and DC meter, got 12.1v under load, 13.6v with no load, and 0v AC load or no load so no AC leak or excess ripple.
Using the handy AC outlet tester, it confirmed the AC outlet and the surge suppressor has the correct hot, neutural, and ground wiring so it's probably not the house but either with my PC or my speakers.
The only thing I noticed is the sub woofer is very loud even if I turned the master volume and bass all the way down. Almost as if AC is being fed directly into the speaker?
The last set of speaker didn't hum but it was only battery powered stereo speakers you could find for about $10.
I've taken the speakers back for an exchange but the problem didn't go away so it is very likely on my PC side.
Any idea? My PC sits on a wood desk and I have carpet under all. The thin stuff you usually find in office or school, not the thick ones. The speakers are all plastic house with no metal connection, and the woofer is all wood box with plastic control panel, no exposed metal.
Nearest radio tower of any kind is about 3 miles away for AM stations, and nearest cellphone tower I know of is about 8 miles away. My room has 1 halogen lamp and 2 regular incascedant lamps no fluorescent lamp they tended to annoy me.