I had that same problem with my trailer. I took it to the dealers and they said I had no output to the speaker from the head unit. Could be your problem.
After that I switched speakers outside to be sure it wasn't the speaker that was bad.
After that I started tracing the wire that ran overhead down behind the microwave, (which I removed) to see if it was pinched, (which it wasn't there) then I removed an outlet under the upper cabinet to see the wire coming from behind the microwave to the speaker, which I couldn't move. So I lightly tugged back and forth from the back of the microwave to the outlet, till it broke free. Funny thing, it worked and has worked ever since!
Hopefully you won't have to do that! Good luck and let us know.
2010 Rockwood 8317ss
2007 GMC Yukon XL Denali 6.2L
Prodigy Brake Controller