Thanks! I have also speculated that it could be the inner pipe of the double -walled header but the noise has certainly decreased. It's conjecture but since the noise has decreased, safe to say I am lucky and it may not be the inner pipe.?
Will def keep an eye on all this and report back. When it completely cooled, I tapped on it with a rubber mallet and did not hear any noise indicating broken inner pipe?
But...I've been known to be wrong at times. Ha.
Jeffrey Alexander