I have an amplifier, which I use as a speaker. I have a few pairs of headphones. They all behave differently.
This started happening when I first changed my graphics card and monitor cable to DVI from the standard analog thing. At first, when I plugged it in, I turned the PC on. Now, I do not remember the exact timeline of the events, either my PSU immediately failed, or I first noticed that something was wrong with my speaker, IE, it was making a high pitched, interference like, noise. Now this chinese crap I used as a PSU, I knew would fail. So I went and replaced it, noted that the sound doesn't work, went and bought a sound card- and it worked.
Again, I am not sure if it worked with speakers, or my headphones. I tried the motherboard sound plugs with my headphones, but I get no sound at all. And now (or always was the case) when I try the amp in the internal sound card I bought, I also get the noise.
So I figured, ok, it's the graphics card. So I plugged the old one in, nope, still making the noise. Then I literally removed every extra component, checked my motherboard for damage or shorts (could not find any spots to indicate the previous) made sure the cables are not tangled, changed around the sockets on the power strip, and nothing works. I turned off the C#s, speedstepping, and I am not really sure what EIST is, but I am fairly certain I got rid of it as well.
I am at wit's end. I don't know what to do. I also noticed that the frequency of the noise on the amp changes when the CPU is under load, and there's a slight buzz/pop when I move the mouse, but this is not always the case with the mouse. Sometimes it does it, sometimes it doesn't.
I changed to linux, and it also does the same thing. I know the amp works fine, I tested it elsewhere, and the headphones are silent as well on the motherboard sound card, on Debian and Windows. I would really like to get my 24bit sound back.
As a note, I would really like to avoid investing money into the solution, until I've tried everything to rule out ground loops. I know the adapter is not that expensive, but with the graphics card, thermal paste (because I removed the CPU fan to clean it up when the PSU failed), and PSU all add up to make sure I am tightening the belt this month.
To reiterate, I switched back to a configuration I knew that worked, and still the problem persists. I have a plug and pray USB mouse and keyboard, and no wireless components other than wifi which I tried turning on and off. I also notice some low interference on the headphones when.. CPU load is high in the absence of other sound. For example, I could load up a game, and it would buzz and crackle, but the moment sound plays it goes away. My motherboard is an ASUS M5A99X EVO R2.0.