tanny whine

Hello everyone:

I'm just about to purchase a 1994 325i with 120,000 miles on it.
It's one owner. Car's in perfect condition except for:

A very slight whine out of the tranny area: Could it be drive line?
That's what the owner thinks. If so how much does something like that cost to repair?

Thanks
See ya,
DAVe

!st, what model is it, and which transmission do you have + exactly when and how does the noise occur?