I am still banging my head against the wall. Cannot find the INTERMITTENT noise. Sounds like an exhaust leak. Two friends who are mechanics, really good ones, also said exhaust, after they listened.
I pulled the pipes. The seal to the efe valve was a little leaky.
Fixed it. Noise persists. Gear or park. Certain rpm range only. Not when cold. Not when hot. Just when almost warmed up. Could this be tranny-related?
The 1st owner of this car had driven it w/o a working speedo cable for almost 12 years. This means no lock-up for 40,000+ miles. (the cruise broke the cable, and he was too cheap to fix it.)
If cooked, the pump or converter wouldn't have an exhaust-leak like soft-knock, would they? The filter and fluid have never shown any indication of problems. And, I have been using Castrol full-synthetic ATF for the 5 years that I have owned it. The last fluid change, I switched back to regular ATF, so there is obviously a mix of fluids. They are compatible, though.
The key is that the noise is NOT constant. I would expect a transmission noise to be constant, with the exception of a clogged filter problem, which almost always changes with warm-up of fluid.
NOTE: I can run the car in the driveway. Warm it up completely. No noise. Has to be driven. Then you can get the noise in gear or park. Logically, the tranny keeps cool until actually driven. Has me worried. I am thinking myself into tranny problems.
Help. Please help. Thirty Firebird lovers have already read this post; someone must have ideas.

Seth

 

This is a ticking sound? Or a louder sound. I assume you put it up on jackstands and listened to it? If not do it.

 

Thanks for your thoughts.
Not a ticking noise. Not at all. More like the soft rapping noise that exhaust can make when being forced through a small hole, or crack.
Every time I prepare to jack it up to take a listen, the noise dissapears. A ghost, maybe?
The noise can get quite loud at around 2,000-2500 RPM. Infinitely more apparent with the windows up.
A noise should appear, and be constant, when the drivetrain is cold. Or when it is hot. But why just at a specific time near the end of warm-up?
Sometimes the noise hangs in there for a while, but ultimately disappears.