Darrick Ball

Bought refurbushed 1993 chevy 4.3lx long block with balance shaft last year. I did the proper 10 hr break in with it. With only 15 hrs it developed this random knock. Only happens on decel and at idle. Other than that it sounds great. Ive heard that it could be piston slap but it doesnt happen when its cold. I did kill each cylinder while it was running. 2 through 6 had no change. Once i pulled 1 the noise was constant. I have a video of it with some good audio . I will attach video as soon as i figure out how to do so. Any info would be greatly appreciated. Thanks you in advance.