I always imagined that the tappet noise came from the adjuster to valve stem interface rather than the cam to cam follower interface. This is probably from working on OHV engines where the cam was deeply buried. I used to find bad lifters/tappets by placing my thumb on the rocker just above the valve spring while the engine was running. The extra damping would quiet down the ones that were too loose or needed attention.
If you suspect one of yours is noisier than the rest, you could try the same trick. It can be an oily mess. But, put your thumb (or dare I say, the body part of your choice) on each adjuster in turn. When the annoying sound changes, you can pay extra attention to that adjuster. Perhaps use the percent of turn instead of the feeler gauge. (I don't recall the thread pitch of the adjuster offhand, to make the calculation.)
I've not known a carb sync to effect rocker noise. A loose cam chain yes, gear train clack, yes, primary chain slap, yes, clutch basket rattle, yes.
So, it doesn't hurt to have extra confidence in carbs well balanced. And, changes in tappet gap effect the cylinder's pull vacuum.
You do know that the goal is to have the vacuum at equal numbers for all carbs after the lock downs are tight?
Cheers,
