Bose speakers

[Msf517]

I have a Bose system in my Denali and the rear speakers are working but the volume is extremely low. If I adjust the fade all the way to the rear I can hear the speakers working but the sound is very low and not high quality, I have to turn up the volume just to hear it. As soon as I bump the fade to the front by just one tap then the front speakers will almost  blow me out of the truck. Someone hit my door a few months back and I had to have the rear door replaced, when I took the truck back to the collision shop he told me the speaker was working but the front speakers were Bose and the rear speakers were standard factory and that’s why they sound so different, that’s when I decided it was pointless to deal with them. Has anyone had a problem like this before? I don’t want to pull the door panel off unless I have an idea what to look for. 

[Phantom 4D]

If I'm not mistaken, that sound system should have 7 Bose speakers. I have not heard of any Bose system having standard factory speakers. Was it replaced at a GM body shop with factory parts?