I've been avoiding listening to the inevitable noise coming from the car.... when the car is warm after a good blast I get a whine from the diff :(. Fine when cold though, can't hear it over the exhaust note. Going to do a gear oil change to see if it helps.
Plan A - Replace Diff
Plan B - Replace Diff and get gearbox reconditioned
Plan C - 6 speed, bigger intercooler, injectors, fuel pump and remap!
Plan D - Replace Diff, sell car, upgrade
Obviously each option goes up in price!