fresh motor , knocks ,then doesnt , repeat

out together a fresh motor for the year and still chasign a few gremlins , i have a knock that if held at say 1500 rpms the motor runs perfect but every few secs its knocks 4or 5 times then nothing, then its does it again , will do this pattern constantly even when it knocks its doesnt effect how it runs , its a slower knock the main rpm i think , motors a 03 5.9 , carrilos , girdle , balanced , bushings in all cam holes , dual pumps , big sticks, its in my puller that has only made two hooks this year any guesses would be great thanks