Shower making high pitch noise

It’s either because of two reasons the first one is the water pressure. The second reason is there is a loose section in the faucet or valve.
When water flows rapidly through a small opening or past an obstruction, it causes vibrations. If there’s an area or section that’s loose, these vibrations can cause the parts to emit a shrill sound. In faucets, something like a slack washer or an untightened screw at the base of the faucet can result in high-pitched screeching due to the tremors.