Before I replaced my hand-held shower head with a HammerHead I removed from it what I think is a flow restrictor. I also placed the head past a little valve so I could change the flow. When the valve is fully open, the shower is relatively quiet and as soon as I begin to restrict the flow to the head it gets pretty noisy. If I put the little restrictor back inside the head will the noise go away? Here's a picture of the restrictor (0.6" diameter):
