The LS motors seem to have a tapping noise with aftermarket cams due to the fast ramp rates of the cam. I've heard people say they have the sewing machine type noise to them after a cam install. It seems to be normal.
Hopefully someone will chime in that can give you a better answer but that's what I have heard.
SOLD:1992 ECSB Silverado lm7 5.3 Swap, TR220 cam, Circle D 3200stall, CBM street tune, Schoenfeld LT's, LS1 efans, transgo hd-2 60e, custom CAI, Autometer gauges
Best 1/8 E.T. 8.86 @ 77.8 on 275/60/15 MT ET Streets with 1.92 60 ft.
2000 RCSB 4x4 Lq9 swap...stock except mild 4l65e....for now