Yes, I have had this problem too- does not effect the brakes and all lights work as well as the brakes, just the little annoying beep. I have finally traced it to when I have been driving in the rain or it has sat for a while in a humid area of the country it will beep occationally until it dries out I guess. Here in Colorado, I hardly ever here it go off. This only happens when towing. Kinda seems in line with what Duck reported above.

Matto