I noticed one time that my tranny got noisier (and weird to shift) with new synthetic fluid. I guess it was just used to having old dirty crap in it. But strangely, when I put type F in on top of the Redline (that I ran short on at the last minute, after draining the old stuff), it was a little quieter.

I'm worried about my trans as well, although the fluid has always been pretty clean. I have shifting problems periodically but I believe it to be more from the clutch, which drags a little bit here and there, especially in really hot weather, or on a steep down incline (I don't get that).

My trans has kind of a funny 3rd gear sound since I got the car 45k ago, but it isn't too bad. The 5th noise is the same high pitched gear whine between 60 and 70 that my brother's car has, although his 3rd gear is very quiet, and his car sees absolutely less than ZERO maintenance. The M47 usually has no problems with 5th gears, but others can be troublesome... I just don't understand these transmissions very well, especially why some make noise, why some make noise in different gears, etc.