my mates selling his car so we decided to rip out all the aftermarket stereo gear currently in his car. all up he had the following in the car:

clarion head unit
6.5" sony splits up front
6.5" sony 3 ways rear
Sony 10" sub in box
alpine 4 channel amp driving 4 speakers
sony 2 channel amp driving sub.

We removed everything except the door speakers and reinstalled the factory cd player. All is ok except the rear speakers sound really strange. Its almost like they are under water. You can heap sound effects sorta ok but vocals and voices on radio are really quiet and you cant hear them.

what could be the problem? All the gear was installed by a shop and we simply pulled it out and rewired the factory HU by matching up all the colours. any help appreciated.