I've got what sounds like a final drive whine and recently it got louder - OK I took it on track. The car is a convertible C5 Auto with 30,000 miles on it. Before I contemplate taking out the transmission, is this one of those things that C5s do? or does it need attention NOW! It's quiet enough that you only notice it with the top up but I don't want to drive it til it breaks! C5s are rare in England and I figered you guys in The States would know if this were a common problem.