[valensds]

I'd say you've damaged your headunit.

What's the manufacturer? There were some pioneer premiers that had some odd issues. My wife has one, and she'll get some occasional fading and distortion. Drives me nuts when all the sudden the music gets quiet, then the bass is overpowering and distorted, then it goes back to normal.

Its possible to damage it if you've cranked it up too loud. I'm assuming you don't have an external amp and its all powered by the deck. The crackling could possibly be a wiring issue, but with the fading you've described I'm pretty sure its a problem with the deck.