i have had this real bad humming noise from the rear of the rav.its crazy.i thought it was the wheel bearing so i changed both the rear wheel bearings. but it was no good.still got that humming noise. any ideas what it could be.
Differential oil (or lack of...)
Noises are difficult to diagnose without hearing them first hand.
Does the sound increase in pitch or loudness with vehicle speed?
Does the sound change on different road surfaces?
Does the sound change when going around a corner?
Check tire air pressure and treadwear. Some unusual treadwear like feathered outer tread can cause noise, as can some normal tread patterns. You can try rotating the tires to see if the sound changes.
As Hachiroku suggested, check the differential fluid level and condition.
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