1WD21 pump on a 4XA59 compressor motor knocking at high pressure
I have a 1WD21 pump on a 4XA59 compressor I believe from 2007. Used very rarely. The pump will have no problems filling the tank from empty and cycling a couple times. An issue arises around the third cycle when the tank is almost full that sounds as if a rod is knocking or a demon is trying to escape from the inside of the pump.
The cycles are more than 20 minutes apart.
I have pulled the head thinking it was a reed sticking but there were no issues. Cylinders look perfect. I checked all lines for any clogs but there were none. Oil level is perfect.
The tension on the belts is just barely off. Would the unloader valve cause this issue? I removed it and did not see any issues.