crackling noise in components

I have been trying to trace a problem through my system. It started with a fading right front channel, which i replaced with new rca's and it seemed to fix the problem until this crackling noise showed up, and then the fading returned.

I have changed head units, and the rca wiring so far. The only other options I have are to check where i tapped in at the floor of my car to run the wires for the components, and the speakers/crossover or the 4channel amp.

any advice would be appreciated its getting to the point where it drives me nuts.

thanks in advance

Try moving your all of your speakers to the rear 2 channels of your 4 channel amp and see if that fixes the problem. It kinda sounds like you have some bad pots on the amp. That would be the quickest way to go. If that doesnt fix it, try and bypass the crossover and see how that goes.
Derl