Basically, you're trying to force the bow to do something it wasn't meant to do. Bows can be tillered to shoot just as well 3 under as split fingered. It's all about limb timing/relative limb strength.
Often, in order to maintain the same nock point on the string and perfect arrow flight with 3 under, the bow will be made to show negative tiller... but it depends on the bow. The key is NOT inherently found in even tiller, negative tiller, positive tiller, etc.... The key is syncronized limbs when held the way it will be shot... regardless of the tiller profile.
Outside of tillering a bow properly to syncronize the limbs, the other option is to raise the nock point, in essence... leave your fingers at the same place on the string, and just move the nock point and arrow from below the index finger to above it. This maintains limb timing, but causes your arrow to leave the bow rather tail high, which it will need to recover from.
I believe the noise you are hearing may be the arrow hitting the shelf as it passes because the nock point is being pulled down toward the now stronger bottom limb in relation to the shelf as you draw. If that's the case, weakening the bottom limb, or raising the nock point should help.
Personally, if I were going to try to shoot 3 under, I would time the limbs of a bow specifically for that grip on tbe string... then I could put the nock point where I designed it to be, and the bow would be just as quiet and shoot an arrow as straight as any other bow.