I have a 6 year old ICP System with a gas furnace with a A coil AC unit stacked above. A couple of weeks ago the fan began to make noise when it turned on. I've carefully/safely removed the fan/motor assembly from below the furnace and I've done the following.
1. Checked to ensure that the noice isn't due to the fan having shifted on the spindle of the motor.
2. Ruled out any debris of any type in the fan assembly causing noise.
3. Confirmed that the fan/motor still is noisy when I run the fan outside the furnace housing.
4. Checked the fan itself to ensure that there are no blades that have come detached. The fan appears to be structurally sound/fine.
The motor is an Emerson direct drive 1/2 HP model that mounts via a rubber cushioned bracket.
The only thing I notice about the motor is that the spindle has a small amount of play or movement in it in the direction of the spindle's axis (in the "through the motor" direction), perhaps 3 or 4 mm of movement.
Is it normal for the spindle to have some play in it, or could that be causing my vibration/noise?
The fan kicks on normally, but after the rpms begin to rise, the noise starts. The fan comes up to speed, but the unit stays noisy.
Sounds to me that there's a good chance the motor is on it's way out, 3 to 4 mm might be a little too much. It has either bearings, or more likely bushings at the end of the armature shaft, where it is supported through the motor housing, and sometimes in addition, a thrust washer that limits end play of the shaft. 6 years may be a little soon for failure, but if it's failed...what ya gonna do.
Some motors have oil ports at both ends of the motor...usually plugged with a small plastic plug. If your have those, you might try a few drops of oil. 20 or 30 weight is usually the norm.
Consider, and call around for a replacement. At least you'll know the ball park price of a new one...and it's always nicer to be proactive and replace/repair furnace parts when it's semi-warm out versus in the middle of the night when it's zero out.
Just because you can, doesn't always mean you should