noisy gearbox, what to do?

right lads the box in my rs has gotten very noisy lately, its noisy true all the gears and its a whinning kind of noise....
the car drives fine but the noise is wrecking me head,
can i get an additive to add to the oil or would a thicker grade of oil help with the noise
cant really afford to change the box again....

their is stuff you get in a motor factors that helps it its in a white 1 litre bottle i thinks it is called lucas its like glue i used it before and it really works if you want me to get you a bottle let me no

I supply redline shockproof red and blue oil 22euro per Lt

free deivery

http://www.redlineoil.com/Products.aspx?pcid=8

ill have a chat with my mechanic during the week about all of the above...
cheers lads