I had that problem and it solved itself very easily. I unplugged the microwave and left it unplugged until it stopped beeping and all the residual power had been used up. I then replugged it in and no beeping! It has not beeped except when it should for almost a week. Apparently this resets the affected board, like rebooting your computer. Few people know about this. My repairman was astonished. It had never occurred to him to try that method.