Automatic Tranny advice/help needed

[Montezuma]

I have a 73 automatic with SUs. The transmission is out of a 77 from what I can see written on the side with the ol junkyard yellow paint pen. The car works fine until it gets warmed up. After driving for a bit, there is a lound click and then a loud sound (sounds like a pop off valve stuck open) coming out from the transmission or engine. There is no real loss of horsepower, I usual drive at anywhere from 65to75MPH and 5000rpms. Does anyone think they know what I am talking about? I have a really good Z mechanic BUT he only has experience with 4 and 5 speed models and detests my auto. He did an auto trans service for me and found nothing of note in the old oil. Feel free to shoot me your opinions and thoughts.

[First Gen Z]

This won't help, but it doesn't sound like a trans noise. I'd look for something else.

[Montezuma]

This won't help, but it doesn't sound like a trans noise. I'd look for something else.

Kinda of what I was thinking too....that is why I threw it on this fourm, your reply to did help....I just want to see what others think too. It always start with the click and no change in horsepower or the guages.

[Arne]

What year car are we dealing with? Does it have EGR?

[Montezuma]

What year car are we dealing with? Does it have EGR?

A 73 with SUs....mmmm...EGR? I am not sure if we kept it or not, but I will look tonight when I get home from work. Most of the smog stuff has been taken off, but the EGR might be there and If it is there you might be on to something.