A couple things could cause this like a faulty pushrod but more commonly a tight valve stem to guide clearance causing the valve to stick for a millisecond when closing. This will cause a big clearance to be present between the rocker end and pushrod which usually bends the pushrod. Make yourself a tool and exercise the valve where the bend rod was and see if it's sticky. Also how many threads are showing on the bottom side of the rocker adjuster where the bent rod was.