I just installed a Pioneer AVH-3300BT and I have no problems with my monsoon.
You should check to make sure your rear speakers wires are properly connected.
As far as the distortion, it may be that your deck is sending out too much power compared to the factory HU's for the speakers...but I don't have this problem.
It may be a feature with Pioneer decks, the LOUD audio option, if you have this turned on to anything higher than LOW---it can cause that extra gain to your speakers to sound distorted at higher volumes.
LOUD is primarily used for lower volumes attempting to keep dynamics of bass/mid/treble!
Any more questions just ask. Welcome to the site!!!!
