Gearbox whine

After an extended session on track (say 45 minutes) my gearbox seems to start whining like a b#stard to the point it sounds like someones snook a supercharger in the back. Is this normal or should I change the gearbox oil for some new/thicker stuff?
It even did it last night in the pouring rain at donny, although I also managed to get pad transfer again and get my tires to go off so I was pushing it a bit. At least I thought I was pushing it until that pesky Craig Dolby went flying past like I was standing still, oh well, keeps me grounded I suppose!

I now get some overun noise since I had the new engine mount infills fitted. but nothing more than that. I would certainly start with an oil refresh.

Yeah go for some better oil. The Redline stuff is excellent. They do about 16 different types of GB oil, so give them a call and they will fill you in on the best flavour for you. They are in Coventry. You normally have to buy it by the case (10 or 12 bottles) we stock it and can sell you just a couple of litres if you wish.