Check the calipers in the rear? I found both sides on mine had broken pads and one side had a loose caliber bolt. I replaced everything, turned the rotors and about three nagging noises went away (not to mention my brakes worked again).
Also, something could be loose in your tags. They work like trailer brakes and have an electro magnet in them...seems like if one worked loose it would make a lot of noise.
If you think it's definately braking (not hitch, suspension, etc) then it's time to pull each wheel an inspect everything, check bolts,, shoes, ads, discs and drums.
1986 Airstream 345 Classic Motorhome