[Valhallatier]

I just bought a bottlehead crack, i plug it to my ASUS xonar essence stx soundcard and to my surprise, i hear a humm or buzz like an insect flying by your ears. its not loud, but noticeable and annoying. the buzzing also occurs if i scroll with my mouse.
some buzz are eliminated if i unplugged the RCA from the amp, but the humm is still there. Can anyone help me?
I use it with HD650 and dt880 btw.