Rear speakers and factory sub-woofer not working

I have the XL 1500 model.
Just the other day, the sub-woofer and rear pillar speakers stopped working. There was a crackling sound from the speakers, accompanied with an electric burning smell. Then nothing. I heard that there is an amp to some models. But I have not seen it either under the center console or under the drivers side rear inner paneling. I have not found it. There is however a fuse that is labeled radio amp. This fuse is intact. Please help me figure this out. Oh and by the way, I also have the rear radio with two headphone but that "module" has not worked since I bought the truck. Well hope that is enough information. Thanks in advance.