Problems with head unit

I've been having problems with my head units the past few months, when its on all it plays, no matter what setting or input, is static.  There will be a little bit of music music, but its mostly just static.

I originally had a Pioneer in, which is where the problem started, but after redoing all the connections, checking all the fuses, and taking some electrical contact cleaner to the plugs it was still there.  I also have in pioneer speakers, all around, and I took all of them out, redid connections, swapped back in the stock speakers, and no matter what I did, nothing worked.  I then bought a new Alpine, and after redoing all the connections again, its still there.

At this point I'm thinking its the ground, but does anyone have any other ideas?

Thanks!

List the vehicle year, make ,model, does it have a hidden factory amplifier?

Thanks for the help, does anyone know where the factory amp might be?  If its somewhere easy to get to, I'm thinking it might be easier to connect the head unit wires right to the speaker wires there.  And no, I didn't use a diff. converter

If there is a factory amp. To me it sounds like its not getting turned on, so that means there must be a remote wire for it that you need to connect to your HU.  Its probably a blue wire on the connector that goes to you factory HU.