I have a problem with my Proform 730 SI treadmill. It is not a load
problem at this point. I have removed the belt that drives the
treadmill, so I am now testing without any load on the motor.

Upon starting the treadmill, the motor starts up as expected but then
begins making an intermittent noise every couple seconds and doesn't
run smoothly. I thought it needed a new motor and replaced it, but it
still does the same thing with the new motor. After running
erratically for awhile, it sometimes just quits altogether. At that
point, start it up again just does the same thing.

Obviously I'm no expert in electronics. What could be the problem?

There is a plastic disc on the shaft of the motor that appears to
provide feedback to the controller board and help regulate the speed
of the motor. At least that's my impression of how it works.

Any help is appreciated.

Thanks.

Mike