1986 GMC truck making a loud noise

[riley2838]

when I start up the truck it is very loud, after if is running for awhile it quiets down, kinda sounds like the muffler noise but isnt constant, and I cant find any holes or pipes rotted or disconnected, any ideas what it might be?

this truck is fully re-done and in excellent shape except for this noise problem, the catalytic converter was just replace within the last year, but when replaced it was "empty" they said, could this be the problem again?? As you can see I have no idea about this stuff, but I want to be somewhat informed before I go to the garage, they could tell me anything there!! and it would usually cost big bucks.

thanks for any help

[bailey]

usally it the exaust manifold to tail pipe gasket leaking.