I think there are two seperate issues being discussed in this thread. What most of you are talking about is the mild popping heard when a car is slowing and there are pressure changes in the system. I've noticed my exhaust likes to pop a little when the MAP sensor is reading less than 3 psi and I get back on the gas. The last car I had did this too and it is completely normal. What he is experiencing may have to do with that, but it may also have to do with his tune. I've heard of TSB's issued on '00 F-bodies for running too lean from the factory and what not. My suggestion would be to find someone with Autotap or some diagnostic software and log some runs around town. Until you can get some good solid numbers, you'll only be able to guess what the problem is.

 

That 'cackle' is normal. I bought my 02 Z28 brand new and it's done it ever since. It's only when it's cold. Don't worry about it.