Audio Crackling/Power loss help

Hello friends,

My gf's 2007 Aveo was bought used with both the passenger front and rear speakers (right side) having some issues. The symptoms were cracking with bass, low volume and distortion. I assumed it was the OEM speakers so I had those replaced. No cigar; same issues:( I then figured it was the head unit. Found one cheap used, same issue continued, just as before. Finally, I deduced that it must be the wiring, so I re-wired and soldered new connections. Same issue, you get the idea.

I'm at a loss:confused: What could be the problem? If anybody can point me in the right direction, I would greatly appreciate it.

My current solution is to wire the right side speakers to the the input from the left side, which works perfectly. However, I think I will lose any speaker balance control, power for wiring in parallel and quality (maybe?)