I had this happen to my bike about four years back. i took the wheel off to have a look after reading about this problem. My diff and drive shaft was very dry and damaged. i went to dealer and they said it was fine and they where not required by Triumph to lube it,Well i went straight to the top man here ,who in turn went to UK and they replaced my diff and shaft, Triumph all so said the shaft and diff should be lubed at tyre changes as a minimum .I have since had no wear or trouble since, i lube at least once a year ,