I am having trouble with my 1969 M20F buzzer alarm going off 10 minutes or so into flight and will not go off until I land and idle the engine completely down. The sound somewhat fades away as the vaccum pressure light comes on. Then as I speed the engine back up the buzzer will again come back on. I activated the stall horn on the ground and popped the breaker out while it was buzzing and that sound went away. That same breaker does not take away this buzzing sound. So then while this buzzer was going off in flight I slowed the plane down to idle without the wheels down to see if that sensor was the problem. I clearly heard the gear horn go off as it was a little louder but the same sound so I don't know that this is the problem. Whatever it is it seems like it takes about 10 minutes to warm up in flight and it won't go off until the engine is completely idleing.
Any ideas what I have going on?