Patient is a 400 chevy that has been sitting in storage for about 3 years. I just installed it in front of a turbo 350 trans. Engine fired right up. No smoke. Engine quiet until hot. When I put the car in drive (when engine is up to operating temp), there is a clicking / knocking sound. Sound is only present on acceleration / under load. Put the car in neutral and rev it and it sounds good. While crusing, the noise does not appear to be present. Has good power and no misses / backfires. Could it be a lifter even though it is quiet when cold? Also, could it be in the trans? If it did it cold, I would probably replace the lifters, however, I would like some opinions. Thanks for any advice.

 

What do you have on it for exhaust?

I'd suspect an exhaust leak at the port to manifold/header.