Engine knock that is not consistent with rpm. At idle can not hear a knock but at about 1/4 throttle I can hear a knock about every 3 seconds. It gets quicker with higher rpm. Changed the oil/filter but still knock. Can really feel it by putting hand on starter. Starter and flywheel appear ok. Sent my son who works for Cat the oil filter to open it and check for metal shavings. Any ideas on what direction to go next? Son lives quite a distance from the farm.