[Greg Reid]

I had the same thing. Chased it for weeks, replaced wp, removed belts one at a time, etc...What was really confusing was that either belt removed reduced it but didn't get rid of it. Both belts off quieted it. I noticed that it was much louder when I listened beneath the front end. That's when I reached up and found one of my crank pulley bolts missing. Reached for the next one and I could spin it with my fingers. The other two were tight. I mean it sounded like a serious knock but it was just the two loose bolts that did it. I actually have a clip of the engine running. I'd post it but couldn't figure out how.
Replaced the missing one and tightened the others and that was it.