Speaker question

I just installed new speakers in the rear of my 03 tundra non JBL with only front tweeters I noticed my left rear speaker sounds more muffled than the right not by a lot just a tiny bit different

 

First thing that comes to mind is that speaker got connected backwards/reverse polarity or it came from the factory wired backwards. What happens if you fade from front to rear and/or balance left to right?

 

If I fade them it's almost unnoticeable but then it throws the front off almost feels like they aimed to surround it to the driver it's more noticable from the passenger seat

 

Yeah my suggestion would be to try and test the polarity of that one speaker using a multi-meter or polarity tester (cheap nifty tool same concept as using a battery).