Are there any solutions or troubleshooting tips to minimize the vibration and loudness of the gable-mount power fans?

Installing rubber grommets into the gable fan frame's mounting holes can help minimize vibrations.

(The following suggestion is from a customer) "I couldn't help but notice that there was a fair amount of motor vibration transmitted to the surrounding studs that the fan unit is screwed to. Consequently, a pronounced resonating hum could be heard (and felt) through that entire wall of the house, both inside and out. The solution to this was to isolate the fan housing from the studs by installing rubber grommets into each of the fan frame's mounting holes. I was very surprised in how effective this turned out to be. Vibration no longer transmits past the fan housing, and the resonating hum inside the house has all but disappeared."