Hello, Tracing down strange sounds in plumbing can be difficult as sound travels much faster in plumbing than it does in air. We’ve had strange sounds come from the pressure reducer outside! Is there any way to get a recording of the noise?
I think I would try to isolate just what causes the sound, like hot vs cold and high flows , like you get from the tub spout vs sink faucets. Do any fixtures consistently make the noise? Hope that helps as a start.