I replaced the rear axle lube in my 2002 PreRunner with Mobil 1 Synthetic Gear Lube 4000 miles ago and I now have a "Rrrrrr" sound from the rear axle. Also a "thunk" on right-hand turns.
Axle code is B04A.
As I bought this truck used, I don't know what lube was in the axle previously.
Initially, I thought the "whine" was from the Michelin LTX M&S tires that were installed at the same time. When I removed the Michelins and put the Coopers back on the rear, noise is still there.
It looks like Mobil 1, Royal Purple, and Amsoil do not make a straight 90 weight synthetic gear lube in consumer packaging.
Any suggestions besides going back to 90 weight dino?