hi all we have a 97 a3 sport with the boss set up, and i have wired in a after market hu,the problem we have now is when the hu switches on, there is a "pulse" "pop" which ever you like to say from the rear speakers, does anyone know why this is? or how i can stop this? as am woried it will blow the speakers as it is very loud. also even when the hu is not on, there is interferance in the speakers, (a whine type noise.) any help is greatly appreciated. thanks.