Toilets, Sinks, Showers, Tubs and Disposals - unintentional shower massager

I have an American Standard single shower fixture. Water pressure is low to begin but once warm water is selected the stream of water begins to pulsate accompanied with loud noises coming from the pipes. Full hot and cold is fine. All other fixtures in the house are fine.

Sounds like there is alot of air in the system. I will move your thread to the plumbing area to get more attention.

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Hello,
I would say from your description and my past experience you have a loose washer someplace in a valve in your piping. Usually it would be closest to the fixture causing the problem. Either in the tub and shower valve or a shutoff valve leading to it.
when the faucet is fully opened it doesn't happen because the high water flow keeps the washer open, but when not fully open the washer will chatter back and forth causing a water hammer type effect or sounds like a jack-hammer is on the pipes.
If you have ball valves in your piping they should be fine its the kind with the round handle called a stop and waste valve that is usually the culprit. But it could also be happening from your shower valve itself. Unless you are real handy you may want a plumber for this one

Good luck