I have a 98 durango w/ 5.2 and the interior and headlights have starting dimming then getting brighter while the truck is running, it does it parked and driving down the road, I don't know if its related but my subs are slowly moving up and down when the radio is turned all the way down too. Could it be a battery or alternator problem? the truck starts and runs just fine otherwise.

 

How do your battery terminals look? Take the alternator in to Autobone for testing...

 

Yeah if your amp is powerful it probably has drained your battery... hints the dimming lights. Can you figure out what voltage the battery has with the car of and doors open and with the car running ? it sounds like a low batt cell

 

Clean your connections at the battery and ensure they are tight. also make sure the ground strap at the frame is tight. If this doesn't fix your problem it would be pretty safe to assume that you have either your battery or alternator going out. Autozone can test the battery and alternator for you but just make sure you have solid connections to and from the battery.