i did my rear bearings last month. i diagnosed it from the sound of a hum at about 80-90km that didnt go away with revs. and also could hear it when i spun the wheel by hand in the garage (awd makes this tricky btw
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i did the labour myself but got a mechanic to press bearings into the hubs. bearings were $170 and so was labour charge - which is a bit of a rip off i think.