Are you plugging a Quarter inch TO eighth inch jack into the headphone out? It is the black one right next to the white RCA out.
Type in quarter inch adapter if you don't know what I mean.
It may be that it is in fact amping something, try the E17 by itself to see if this issue is a fault E17
Nope, most full size headphones that someone with the E17 would generally buy come with a removable Quarter inch headphone jack where when you twist it off, becomes eighth inch. Those that can't thread off generally shouldn't be used with the e17
It may also be the E17 in the position you are putting it with some cables are getting EMI
That cable doesn't seem out yet.
I'm using a quarter inch adapter into the headphone out on the Asus card, that's correct (I did not know the jack sizes in inches, thanks). I've tried the E17 through USB so the noise doesn't seem to be the fault of the E17. Also, when i use it as AMP/DAC with my Ipod, there's no noise at all either. I guess maybe i should get a proper cable to use with my PC.. maybe even use the SPDIF/Toslink out.
And regarding headphones for the E17, what do you mean when you say "thread off"?
Thanks for putting up with all these questions! ;)