My observations as a bowyer and shooter.
1. Shorter the bow, more index finger pinch on split
2.Less fingers on the string, better release and flight
3.You can manipulate bow noise by moving the nock,adjusting grip( on straight handles) and string weight.
The A1 thing to remember here is "where is the center of your bow". Where did the bowyer put your fulghram that the limbs are braced against.
There are mulitples scenerios that one could be creating here. Your string grip, center of your bow, limb weight and grip are the big four.
What causes bow noise? The uneven collapse of the limbs. Simply one is faster than the other. String silencers help dampen the vibration.
Why does a heavy arrow shoot quiter than lighter arrow? It slows the speed of the limb collapse down more.
Oh heck I better quit, i could go on and on.
My suggestion is take a mechanical release and mark on your string an inch above your current nock and mark 1/8 " imcrements down 2 inches. Shoot 3 arrows at each mark. pick the quietest one. Remember though the middle finger does most the pulling no matter what grip, 3 under or split. So when one shoots 3 under , they basically move the string breaking crease down inch. This is why 3 under is almost always louder.