You don't mention front or rear, or whether switched into 4x4 or not? Nor do you mention having both sides of the same axle in the air at the same time?
Depending on the above, you can verify whether or not you have a LSD and whether it's normal or not. It is possible to tell from the presence of a ABLS system, in which case the opposite wheel should spin in the opposite direction, due to a normal, open differential being incorporated on the prospective axle. Someone may be able to tell you in which year the introduction of the ABLS system took place, I am unsure.
Way too many variables to tell so far.
If your mechanic is to be trusted, and advises you not to worry, you have no mechanical issues, so chill for now!
Na, don't do that yourself, best take it to the garage.