Help!
Our 2000 Impala w/3800 V6 is making a ticking/rattling type of sound upon startup in the AM. It goes away (or gets so quiet you can't hear it) when you put it in gear. After a few miles of driving, the sound goes away entirely.
I first heard this noise during the warranty period and the dealer could not reproduce the problem. Then the transmission failed at 46K, and we had it rebuilt. After the rebuild, I noted the noise again and called the tranny shop. They suggested it was probably an engine problem, so we took it to our maintenance shop and they could not reproduce the noise until my wife came to pick up the car and started it up. They listen and are quite sure it is a tranny issue. So, we take it to the tranny shop (which also has an full-service engine repair shop next door) and they can't reproduce the problem until my wife goes to pick up the car. They get an engine guy and a tranny guy out there to listen and they believe it is an engine problem. We bring it back to them a couple of days later so they can cold-start it, and after some diagnosis, the engine guys send it back to the tranny guys. The tranny guys then proceed to pull the transmission, replace the pump and the TC, reinstall tranny and THE NOISE IS STILL THERE.
They state they are stumped and don't know what could be causing the noise. I call the dealer and ask about "piston slap" as a possible cause. "not on the 3800" he says.
Has anyone seen this issue before? What could be causing this rattling noise that goes away when you put it gear and drive a little.
Sorry for the long-winded post. Thanks in advance for any ideas. We are at wits end.