Rear Deck Speakers

Check to make sure the front/rear balance on the audio setting isn't set to full front. I know of no other control to disable any speakers. If all is OK there, check to see if the wiring to the speakers hasn't become damaged or unplugged by large items placed in the trunk.

That's odd. I wonder if maybe the rear deck speakers are used only for the noise cancelling system. I'd go to the dealer and check another car on the lot with the same audio system to see if it works the same.

I just went into my car to listen to the rear speakers. These are pretty much subs which won't have much if any midrange content like voices and instrumental notes. If your bass control in the tone settings is set to minimum, you won't hear much from the rear deck speakers. Crank up the bass and play some music with a lot of bass content. Bass is non directional, so you might not be able to tell it is coming from the rear speakers even though you can hear/feel it. Go into the trunk and gently touch the cones of the speakers to see if they are vibrating. If not, I think you should see the dealer.

I forgot to mention that I have the Bose system, but it should probably work the same in the non-Bose setup.