Diff just started whining!

Optimiser

A few days before the whining started I drove over what turned out to be a piece of square steel tube about a foot long that I thought I would clear! Big FAIL!!! I went over it right in the middle of the car and there was a couple of big horrific bangs! The car kept driving normally and there were no new noises. I has a look underneath and saw that the rear tunnel brace was a little damaged and a small dent in one of the exhaust pipes. After an inspection by my mechanic I'm told that it appears that the end of the tail shaft/front of diff was hit by it. This has somehow damaged the front diff bearing which is now causing the whining noise after a few days. A small camera was poked into the diff and the crown wheel and pinion appear ok, but the diff will have to be taken apart to fully check, have the bearing replaced and anything else that may be damaged and then all rebuilt again. The drive shaft itself will also need to be checked and possibly rebalanced.
I would have never called this!