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I have an AT JB74 for about 3 years now with 60,000Km/37,000Mi.
My rear differential making a humming ("whoOomwhoOomwhoOom") sound everytime I cruise (AT on 4th) on 1500 RPM 60 Kmh/37 Mph and 3000 RPM 100 Kmh/60 Mph, but it's not there if I turn off O/D and use 3rd and match those RPMs. I think it might be the 4th gear group. The shop hasn´t resolved the issue and it's been there since year 1.
