The drivers cannot typically be repaired and the bad news is they are no longer made. At present I have 2 known working used drivers on hand, they are $40 shipped. However, a driver that beeps, usually works unless there is some obvious water damage, a faulty driver tends to not beep and get very hot. If you have a watt meter a faulty driver will usually show a very high watt draw 150+ and usually around 400. My guess would be there is something wrong with the drive unit (propeller assembly) and one driver has a lower alarm threshhold than the other. If the drive unit is a few years old it may just be time for a new one. The most common cause is a worn or stuck upper bearing- part 3000.610.