JBL Sub ?

Hey guys,
I've done some searches but haven't found an answer to my question. I've just purchased an 07' Double cab with the JBL sound system. The rear speakers and sub sound muffled and aren't putting out much sound. Just curious where to start searching before I tear everything apart? Does the factory amp have any adjustments that can be made? Thanks ahead of time!

 

I know there is a TSb for something with the sub might want to check that.


http://www.tacomaworld.com/forum/2nd-gen-tacomas/7107-tsb-list-2005-2009-toyota-tacoma.html

Abnormal sound from JBL sub.

My sub is located behind passenger rear seat. (incase you didnt know I didnt know until I was searching for something lol)