(air?) whine from heating system fan?

#1
(still hunting for a used one of these).

I drive a 2012 yesterday and there was a high pitched whine from the climate system with the fan blowing. It was worst on cooler A/C settings and went away if I moved the temp selector past the center towards the warmer temps. Definitely air flow related as it was louder on higher fan settings although the fan noise tended to cover it by the time you got up to a "4". Didn't really sound like fan motor, more like air. All vents were fully open.

Known issue? Or something unique?
 
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