First Of All I'd Like To Say Hi To Everyone On Here... I Recently Bought a 03 1.8T Quattro. and i must say i F****** love the car.. but i haven't had to pay to fix it yet

I Seem to have a problem with my head unit, I believe, im only getting half volume to my rear speakers and its like my sub is completley off.. i've adjusted the fader in and out, and the front speakers are only working, does anyone have any suggestions? i have the dension ipod adapter, so maybe they bumped something when they installed it. i've only had the car a week, so i don't know much about it yet.. but im pretty good with electronics, so im hoping someone might have a little idea on wat might be wrong...... if all fails i guess im gonna get a Double Din Dvd Player sooner then i thought

 

Anyone? this is driving me nuts.