Stereo and speaker problems help please

[01jetta]

I have a 01 jetta everything stock (because of this problem) I have an aftermarket HU though. Ok so I have had a problem with the car dying over the period of a couple days of not driving or sometimes overnight. So I took out the radio and it still had the problem so I disconnect the radios harness to the factory harness and my car doesn't die anymore. When I have the aftermarkets HU harness connected the speakers play static even when the car is of not loud but enough to hear them that's why I thought it might be the speakers. The factory speaker wires go to an amp in the back a monsoon. I have no idea what's wrong any additional info needed just ask any help with be greatly appreciated

Thanks, dj