My airhandler on my furnace is noisey. It sounds off balance. I had the same issue over the winter so I cleaned the blower wheel and that helped but I've noticed after a month running it this summer it's doing it again. I cleaned the wheel again and that didn't help. I can't find any oil port on the motor to oil it. Any ideas of what could be causing the noise?
Thanks.

Possible fan is out of balance,if this be the case not much to do but replace it, might pull out the squirll cage and give it a real good cleaning,, most/very few/almost no motors have oil ports

When you clean this fan what are you getting off it? Are you using a good filter prior to the fan?

If you are getting rimey chucks then you ned a better filter. You can buy a spray for the filetr than puts down a sticky mist to filter better.