I think I can here ya KNOCKING!

Also check your bottom pulley bolts to damper. Makes a nasty sound when they are loose also.

Could try and see if damper will move fore and aft. Would be thrust bearing.

Rapid knocking at idle? Rod wouldn't be rapid at idle, but then again, don't know your definition of rapid compared to mine. I'd check for starters teeth to flexplate, flex plate teeth to something else or, and this happened on a new motor (sickened me till figured it out ), crank throw hitting dipstick. Sounds like a rod knock.