Going through some other items on friends boat and horns just make a thump sound when pressing button. I have not torn into them yet, but what typically is the issue's with these? I'll assume the diaphragm's are messed up. But seems odd to the fact they both are doing the same. Hand on the rear of horns and can feel they are both thumping. Could even be full of bug nests for all I know. I'll do a quick check for 12 volts making to the units, then next I'll looks down the tubes for mud dobber nests. Anyways...if someone else has had similar issues, I'm listening. Thx for any others advice...DM