Bearing problems are difficult to diagnose without a test drive until they're literally falling apart. On the test drive, throttle position will usually make a difference in pinion bearing noise. Most pinion bearings (the ones behind the driveshaft) will make more noise with power applied than they do when coasting, and the noise will really diminish at a "float" where the engine is neither pulling or coasting. The carrier bearings are the ones that support the differential assembly and the ring gear, the big bearings at the sides of the housing when the cover plate is removed. Failing carrier bearings will have a pretty constant hum regardless of load, and the noise will increase with speed- - - -faster road speed, more noise. It's hard to separate carrier bearing noise from axle bearing noise - - - -they turn at the same speed. Then there's gear whine- - - -a whole different can of worms! An experienced diagnostician can tell the difference, but it's almost impossible to describe slight nuances of noise with a computer keyboard. Test drive about a thousand cars and repair the problems you find, and it gets a little easier!
Jerry
