MGB Noisy Rear Axle / Differential

I have a 1967 MGB Mk I Roadster which I used for a recent track day. The car has a banjo rear axle and I am trying to track down a problem that has arisen with it.

Driving home after the event I noticed that the rear axle had become suddenly noisy, with a pronounced "howl" that increased in pitch with speed. I do not believe that it is gearbox or prop shaft related.

I understand that there are a number of potential causes for a noisy rear axle, but I am having trouble identifying which it may be, and am therefore seeking suggestions as to how to trouble shooting the cause:

• Thrust washers were replaced about 10,000 mile ago, but my understanding is that these are more likely to result in a differential "clunk" than whine
• Rear hub bearings?
• Differential outer or pinion bearing?
• Differential bearing
• Worn / damaged crown wheel or pinion
• ??????

Any suggestions for tracking this down would be much appreciated.

A "howl" without accompanying clicking or rattle usually indicates pinion/crown wheel misalignment. But a bearing can also be the culprit. Only sure way to know is a tear-down and inspection.