Hi I have installed the pioneer avh5200bt to my aud s3 8L on an X plate, it come with fully amped bose system so the amp and 2 subs in rear etc i bought the following lead off ebay to keep everything the car Bose related working as normal - PC9-408 Audi Porsche with BOSE System Car Harness Leads on eBay (end time 05-Jan-11 16:06:37 GMT) it seems to do its job all speakers are working amped and subs are working fine. The problem i am having though is even when ther is no output im getting a hissing noise from the speakers sounds like its coming more from the back than the front if i turn volume up with no output the hissing gets even louder. When i play music from my ipod or a dvd etc sounds good but still slight hissing obviously heard less when volume is louder. The head unit is mean to be 4 x 50 w Mosfet which means its amped i think, my opinion is the head unit is sending an amped signal to the bose amp which amps the fequency again to create the hissing, doe this sound correct? If so how do I stop this can i stop headunit amping, surely loads of people connect a new head unit amped to a aftermarket amp dont they ? Please can i have your opinions would be much appreciated if you have an idea of something else it could be or how to fix this . THANKS CHRIS