I have a 2004 F-350 powerstroke Crewcab. Last year the factory radio went out, so I purchased an aftermarket unit. It worked fine for about 6 months, then started popping through the speakers and it increased with frequency. The radio finally went out, and was replaced with another after marked unit, from a different brand. it has started to pop after a few months. Both of these included a harness to maintain factory cab wiring.
What could cause this? as far as I know there is no amp, and if the amp was causing this, could it take out the radio.
Also, the beep from the car when locking the doors has recently stopped as well. The doors all lock properly, but no sound from the horn when locking.

This had the 6 disk radio in it. Is there a factory amp in the truck?

Thanks for your help.

 

It could maybe be a bad ground