lol

best comment on earth

thats not the headphones, thats just quakelive...

Maybe the sound is too loud?

I had same problems with 7H and I changed some settings in my soundcard (asus xonar)
I enabled AEC (Acoustics Echo Cancellation) and other options got disabled.
Hope you can work something out in your soundcard settings.
Try turning green audio port cable slightly as well in case bad connection.
It happens to mine.
Anyway GL

AEC is a microphone function to reduce echo in the front speakers while recording

It is funny that my sound started working perfectly in game.
I could not notice them before in all 2ch 6ch 8ch mode or changing sample rates to 92 192khz and my sounds were fucked up.
I couldn't figure out where where enemies coming from.

I got onboard sound :-/

but still stereo worked on my sennheiser pc161

Something causing it to playback in mono?

in my windows settings it says "stereo"

Try the usb. See if the problem persists. If so the jack might be defective or the cable might be broken.

there is no USB connection :D

does your soundcard has some "3d sound" options?
disable them, or try to put the soundcard in speaker mode.