My usual googling skills have failed me on this occasion. When I set the volume extremely low in foobar, I hear a weird sort of hissing noise/distortion whenever a note is audible in the music. Turning the volume up either removes this noise or drowns it out – either way it becomes inaudible...

I'm not sure how to go about it though, as I'm not exactly a hardened veteran audiophile. I'm currently using an ASUS Xonar Essence STX with a pair of HD555s. I really don't know what I should be looking for. Help would be nice! So would a cup of tea..