2014 Rear Speakers low sound
 

I took my 2014 Maxima to the Dealer yesterday because there is very little/no sound coming from the rear speakers. They used to have sound. The dealer service guy turned the fade all the way to the rear and turned the base up, and there is a little sound/vibration, so they said they are working and nothing they can do. I do not think they are working because even then you can not hear enough to tell what song is playing. So much for the dealer service.

Anyway, the problem is that even with fade turned all the way to the rear and the volume turned up, you get some sound from the door speakers, but none I can hear from the rear window speakers. Can anyone help me fix this DIY style since the dealer can't?