[M.D. Holloway]

I have seen where VFDs that drive compressors and pumps will produce a ultra low 'hum' which will contribute to bearing failures. Many times, to the un-trained eye the culprit will be brinnelling but in actuallity it turns out to be low level vibrations from currents.

I often tell various storerooms and tool cribs to periodically rotate the stored bearings so they don't get wear spots from the 'hum' of the factory.