whining while accelerating

My '99 tdi jetta which I just bought, has a whine when accelerating in either 4th or 5th gear. It completely goes away when you let off the diesel. We were told by the seller that it was a boost leak. Does anyone have any ideas or experience with anything like this, or any ideas on where I would begin to search it down. I live in Newland, NC, near Boone and would also like any recommendations on a good vw mechanic.

If it does not make the noise when you accelerate hard in 3rd (but does in 4th and 5th), then it's hard to imagine it is not a transmission whine.

Graham

check gear oil?

Thank you so much for the help. Do you have a recommendation on the gear oil? I am thinking to just go ahead and drop the old transmission oil and replace it with Lucas.

Stick with OEM. G60 or G70. The later is thinner and supposedly better for shifting with a cold tranny.