Hello And Help

hello to everyone who uses this forum, had a quick browse through and it looks like the best i've seen. Now for the question that i can't find a solution for. I am the prode owner of a bright green A4( a bit like the one in the bp ads from many moons back) Now the problem is the I have removed the standard concert unit and fitted a jvc head unit and cd changer, but my rear speakers do not work below half volume and very low above half way. i have fitted the modified loom from the audio shop but the problem persists. Please help me...