Isolating dc motor vibrations
I'm trying to reduce audible noise from an air quality sensor. A little 20x20x10mm dc fan is being variably driven with pwm. It has an inherent small whine, probably being driven in the low 10s of kHz or having sidelobes there. It's mounted on a plastic plate, so this vibration ends up amplified and shifted to be a persistent hum. Photos included of the assembly.
What is the usual approach isolating noise? It's a cheap component so swapping to a better bearing is fine, but I'd rather just cut a gasket under the fan and screws, or between the sensor box and its mount on the plate. I have already tried a gasket under the fan with some fiber I had on hand, but it's not a suitable material and vibration was not reduced.
I'm down for electronics modifications. I could add some reactance, but I cannot change how the motor is being driven as this is driven by a black box.
Thoughts and advice appreciated, have a nice day.