Bought myself a nice 2001 Rav 4 D4D with 174K miles with loads of service history. All good and looks to have been looked after, but the only thing it is doing is humming/whirring noise at between 40-55mph that disappears at 60mph. It does sounds like a wheel bearing, but garage have confirmed it's not. They had it hung up and listened to the rear diff where they identified the noise. On closer inspection the oil had water in it, froth on top and smelt burnt! Diff oil has been replaced and also Forte diff treatment added, but noise persists. I have read about possible issues with tyres such as feathering or cupping so i'm in the process of going round and replacing each wheel with the spare. The tyres fitted are Cooper Discovery M+S and they have snow icons on the side so look like winter tyres. The spare I'm testing is a Michelin.
I'm interested to see what peoples thoughts are and also if it's worth getting a secondhand diff then the garage fit it.