2003 Jeep Liberty Factory Amp information

I have a 2003 Jeep Liberty. I get a popping noise in the speakers when I hit a bump, and then the sound usualy cuts out (sometimes not all the way), untill I hit another bump. I spoke to a local installer about it, and he seems to think that the factory amp (Infinity) is bad, and wants $70 to bypass it. I have two issues with this:

#1. I can't seem to find the factory amp (he said it was located under the back seat or under the passenger seat). I've looked in both locations, and don't see anything.

#2. I've had aftermarket amps go out before, and the sound would just cut out completely. No multiple pops or static.

I'm realy wondering where the factory amp is, and if instead of bypassing it, if I can install an aftermarket in its place. I am not even completly sure that the amp is the problem, (I'm leaning toward a grounded speaker wire), but I fiqured I would start there.