DerbyDad03 wrote:
....

- New problem, started about a week ago.
- The last modification to the system was a replacement fill valve in
a toilet, but this was many months ago, with many months of no noise.
- Yes, I have a pressure reducing valve.
- No, I have not checked the pressure.

I think that isolating the toilets should be my first (and easiest!)
step.

That can find if it is one of them, obviously. I've had issues w/ the
reducing valve failing in full open spot. Pressure itself isn't the
direct cause of hammer, of course, but higher pressure could be the root
cause of the cycling of a toilet valve. Or, it could be the reducing
valve spring itself chattering as it cycles.

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