Got a new headunit for my audi s3 it still had original Audi headunit in but i Am getting a whining from a rear speaker but its fine with original headunit, i can stop the whining but only get front speakers working. i have the correct audi adapter cable. anyone else heard/come across this problem before? been told could be bad earth? or speaker cable? help please driving me crazy!!! tried earth didnt seem to be that!