68 firebird noise

[sammypoodle]

I have a 1968 Pontiac Firebird. When the car is cold and I am driving and about to come to a stop the car will make a loud clunk. It seems to be coming from the engine compartment and I can feel it in the steering wheel. The clunk only happens just before the car stops and no other time. After I drive the car for 15 minutes and it warms ups the noise goes away for the rest of the day. Any ideas? The engine is a 350 V8 with a 2 speed polyglide automatic transmission. The tranny seems to shift smooth as well as the engine. So I do not suspect either of those two items.