It's amazing, the areas that a sound like this can come from.
I had an engine tick in recent years that drove me batty because it was coming from the low end and varied with rpm but engine load wouldn't change it. Wasn't crank or rod related.... it drove me nuts.
Until I figured out it was the mechanical fuel pump arm slapping off the back side of the crank lobe because the pump arm didn't have enough preload to ride firmly on the back side of the crank lobe. (335 series ford V8)
Small block chev would have a rod between this mechanical pump and is cam shaft actuated I believe.
You never know.....
(assuming it has a mech pump)
