MG Car Repair: MGB differential noise, wheel bearings, acceleration and deceleration

Question
I have a huming noise in the rear of my 74 MGB and I can't tell where it is coming from.  I raised the rear end and tried each wheel seperate and couldn't hear the noise.  Sometimes it sounds like a bearing but it could be the ring gear and pinion.
I also have the problem on the left side rear being about one inch lower than the right rear.  Could this be the shock or rear spring?  

Answer
Hi Wayne,
A noise from the rear end is sometimes hard to ID as the unit body construction of the MGB can amplify the noise of a differential, a "U" joint or wheel bearings. Sometimes I was able to isolate the noise a little by making "S" turns on a road at the speed the noise is most noticeable. The wheel bearings on an MG are ball bearings and side load can alter the sound a lot. A ring and pinion noise can be altered by acceleration and deceleration. However "U" joint noise is also altered by acceleration and deceleration. Carrier bearings in the differential can be altered an little by accel and decel but not much. A mechanic's stethoscope while on a lift used by an experienced differential mechanic is the best way to ID a problem.

While I was at a MG dealership in 1964 we had a BMC rep come to the dealer and wanted me to rebuild a new "B" differential because of too many complaints of differential whine. I rebuilt a new differential on a new car with the rep to try to see what was wrong. I found nothing wrong and later BMC issued a memo to the dealers to undercoat the box area of the body around the differential to lower the noise that they determined was the normal sound of a differential being amplified because of the sheet metal box area it was in.

So the standard method we used was to first drive the car and accel and decel and "S" turn then put the car on a lift to feel for free play and listen with a stethoscope to decide what was to be done.
The ones we determined that were a normal diff noise we just undercoated the body in that area and others we removed and rebuilt as necessary.

As far as the car being lower on one side look at the spring mountings and if they look ok you need to switch springs as the left one is sagging due to driving the car mostly with only a driver in it or replace the springs or have a spring company rearch the springs. The lever shocks on the car do not support any weight at all, they only dampen movement up or down.

Howard