[Rear Speakers not working]

I dont know if this has already been posted, I looked and didn't see anything, so figured I would post it.

I have a 1996 Avalon XLS with a Aftermarket JVC headunit it, and one day while I was driving down the street, the rear speakers started sounding like the sound was coming out of a tunnel, not an echo, but a far away sound. I turned the HU off and upon turning it back on, my rear speakers no longer work. The speakers are stock I believe, not quite sure since I cannot figure out how to get the covers off of the rear speakers. If anyone has ever experienced such an issue, or has taken the speaker covers off the door panel, please let me know how to do it. I need to find the cause of the issue.

[Who has the Avalon with most mileage?]

Hey new to the site, but saw the thread. Proud to say My 1996 has 246,xxx miles on it. Was even in a crash in 99' where it was supposedly totaled, been through 1 transmission. Runs perfect.