I have a 1995 Z28 which has a knocking sound coming from the driver's side header pipe when the car is first starting. Could this sound be from the steel expanding because it is cold? The sound if fairly loud and can be heard inside the car.

 

its not because the steel is expanding. Is it more of a knocking or a ticking? That will help us all diognose it..
Knocking is bad
Ticking can be fixed well usually

 

The sound is definately not ticking. I know what ticking valves sound like. It is a loud plink. Sound are hard to describe in words. It sounds like someone is tapping a pieces of metal. There is no consistent time between plinking noises, but they appear to be about 15-20 seconds apart. Sometimes it will make the noise every 15 seconds or so and the I won't here it again for a few minutes. After the car is warm, I don't here the noise. Maybe I can record the noise with my camera and send it. Sorry, I know this doesn't give you much to go on.