Ok, cool, sounds like it's mainly an issue associated with gaming. Another poster here I read they mentioned the graphics card as a potential reason for the hum/buzz....I've thought of a way you can test this that should isolate whether it's a hardware (associated with GPU) or software driver issue. My theory is that you need to try to run the GPU at 100% load but not in a game, and then you'll come out of whatever is creating your 100% GPU load (and leave that running in the background), then you'd fire up some music in ITunes or whatever player you use and then you'd see if your music plays without a hum/buzz.....this test will isolate if it's just the high GPU load that is causing the issue or not. If it passes this test without hum/buzz then it's probably a driver/software issue. In terms of what to use to create the GPU load start off with the GPUz render test:
Click here where you can see my mouse pointer:
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Then you can open up the Sensors Tab to check your graphics card is under a little stress:
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Now this is quite an easy test for the GPU so you might need to run a different GPU test that uses more Watts. If GPUz Render Test above doesn't create the buzzing sound you're talking about (as you're listening to music whilst running the GPUz Render Test at the same time), then use a GPU stress test that is harder on the GPU: try running Unigine Heaven benchmark on a loop but as a window (
window mode not fullscreen), and make sure you turn off the sound effects in Unigine Heaven benchmark (think that's an option) so that you can make sure the GPU loading program is not asking your soundcard to produce any sound......then listen to music whilst that's running & see if you still get the buzzing sound. If you don't get the buzzing sound then it's some kind of software driver type issue rather than the hardware of your loaded GPU causing interference.