I've been using lucas 85w-140w in the rear end and it has quieted it down a lot. I do ride in a warmer climate here in Califonia and log most my miles spring through fall... Hence the heavier weight oil. It's only 5w above the 80w hypoid OEM spec at minimum but on long rides and heavy use it seems to not thin out and like the fixed weight oil. With a locked rear end and not tight gear tolerances you'll get some noise especially when the gears are not under load.