I have a blower motor on a trand furnace, what would cause the motor to vibrate?

If the motor did not vibrate before but now is starting then I suspect a bearing ging bad or debris building up on the cage. Use a shop vac with a brush and clean off all the fins. Make sure the power is off to the furnace fist. Grab the housing and the cage and see if there is any movement side to side or up and down.

What does open high limit device mean?