'94 Camaro 3.4 v6 : Sounds like pressure build-up or release from od into drive.
Noise stops when shift is complete. Been to two tranny shops. Said it wasn't the
tranny. Had never heard asound like that before. What is it, PLEASE!

 

could be a number of things. you might just be hearing the trans fluid being pumpped through or released.

 

It is a really loud noise. Sometimes I have to go ahead and shift to stop it.