[legion]

Check for shorts in the wiring. A short between the switch and the unit or a short between the infrared sensors and the unit could cause this kind of problem.

Check for kids across the street with a garage door opener giggling.

Also, ten years seems to be about the lifespan of these things. I wonder if the bearings in the motor are worn out (or on their way out) and it sometimes has to work harder--which it interprets as coming into contact with something.

Me?

I'd just replace it. It's usually cheaper (and lasts longer) than trying to source and replace just the motor.