[DonSor]

It's starting to sound like it's tranmission although from what I know transmissions will overheat first and then over-pressurize and start leaking fluid - without making the sound you described. It is in the drive train for sure. What's troubling is the fact that the noise you described sound like either a metal to metal contact or an explosion (cylinder firing) of sorts. My advice:

Go to a reliable transmission shop and describe to them your prolem. They will do a series of test, one maybe pressure test. If they give you the song and dance routine of a 64 point check, beware of a rip off. If it is the transmission, most transmission shops have rebuilt units on their shelves. You don't need a new one. Get some assurance that that will solve the noise problem, and a certificate of warranty. Good lucj.