^ I've heard it before. I know what it sounds like. This an't my first rodeo... lol
I went thru this same ordeal on my buddy's 02 SOM SLP SS with his heads and cam swap. Came from the same area, and sounded the same.. Not the sewing machine noise, this sounds like a knock, but it's deceiving because it sounds like it's coming from the collector or the wheel well area. We thought it was the wrong push rod length so we did THREE pushrod changes, and none fixed the knocking. Then we got a push rod length checker and got the right size. We thought it was dead lifters, so we tore the car BACK apart again to replace the lifters. THEN we did the oil pump O-Ring. The O-Ring fixed it.
There wasn't a reputable, local LS* place out west, so most of the people came to me with their problems. = LOTS of research. Had a very mild vibration on a 99TA that was a pain to locate. It only did it at 1400rpm. Was reluctant to make that call with the car having 115k on it.
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