When it's extremely cold out (under 20 degrees F), low fan speed settings will emit a soft warbly noise that sounds like a light high-frequency squeal. If I increase fan speed, the noise goes away. If I reduce it back to a similar speed/RPM, the noise returns. What is this, just some cold/dry bearings in the squirrel cage fan? Is there an easy way to quiet the fan (add grease lubrication?)?

Does anyone else's fan do this when it's cold?

 

If it only does it when it's extremely cold? I would'nt sweat it.. just keep it at an rpm where it's not making that noise to prevent it from wallering out.

Most likely the motors bearings are a little dry or the grease is a little contaminated.

(the plastic used on the housing and impeller would make more of a rubbing/scraping sound than a squeeking. It 30% talc)

Rich