00 Monte SS Bad Sound

Have a Monte Carlo 2000 SS with weird speaker sounds. I have cd/tape deck and the back speakers are not very loud. I can turn bass & treble all the way up and fade to rear speakers and its barely above medium level sound. There is no bass and back speakers are quiet. Still working to hear them but quiet. What would be the cause of the prolem? Does it have amp or is the box attached between the speakrs a keyless remote control box? ANy ideas? Just bought the car .

look in the trunk under the rear deck there is an amp..if thats your problem or not i couldnt tell ya..the rear spekers arent supposed to be super loud..but loud enough