Default Nexus 7 car install, noise in speakers

Hi

I'm finaly got my nexus 7 connected to an amp so I can get sound out of it.
But when I have no volume on i get en hi noise like intense beeping.
And when i power off (turn of ignition) i get an loud bang in the speakers.

Im using timurs rom
and this http://www.ebay.com/itm/Behringer-U-...item3a8574d60a
For USB to audio.

I've tried disconnecting the rca cables and than the biping sound goes away, but as soon as i connect it to the USB to audio i get the sound in my speakers.
Can it be an faulty unit?