no sound from rear deck speakers 2007 e90

HELP. new to the forum. I bought a used 2007 328i with what appears to be the factory hifi system, two front door speakers, two reardeck and two subs under the seats, no rear door speakers. I get no sound at all from the rears. I have popped the grates and both speakers are wired up. Is there a fuse or something I can do myself that doesn't involve taking it to a stereo place to find out the problem? thanks for all in advance. I have already searched and can't seem to find a solution.