I replaced the motor in my American Standard furnace/air handler last winter. It's worked perfectly until today. There is an occillating noise coming from the motor/fan area. It comes and goes. I pulled the fan and motor and checked all of the mount screws, they were ok. There is a very small amount of lateral movement between the shaft and the motor body, but I seem to remember this was present when I installed it. Any ideas?
Intermittent vibration would be unusual... I would check the fan blade for debris, dirt buildup, or a missing balancing weight... Maybe take it out and spin balance it on a nail in garage.. I had one with so much dust on it one time it would rattle picures on the wall. Cleaned it off and it ran fine.