I sometimes get pops and clicks and have come to the conclusion that it is almost certainly electrical interferance from the computer's onboard sound because I haven't got a decent soundcard atm.
I can turn my system right up on Radio, AUX or CD and there is no crackling.
Just get an uber-bass song on the go, if it sounds naff something is deffinitly wrong, then try with onboard etc, unlucky if it is broke, I couldn't live without my sub