I can't say for sure if your quiver slows your arrow. You'd have to chronograph it as macbow said.
I do know this though. Sound is a product of vibration. Vibration requires energy input. Therefore if your bow makes noise, it is vibrating (or the string), and either way that energy is comeing from teh energy stored during teh draw cycle. The more energy that goes to vibration, the less that goes to the arrow.
Actually, the vibration fo a string or limbs, should be mathematically very similar to the stretch of a dacron string vs. fast flight. The only difference is the stretch of the dacron is damped very quickly (doesn't oscillate like a string vibrating back and forth liek a guitar string).
I don't know if that helped or made things worse.
My advice is don't worry about it, if the bow is quiet, seems sufficiently fast, and shoots well, call it a win.