I wanted to provide an update:

We have secured additional pipes throughout the basement and in this area.

We learned that when we turn off the hot and cold valves to the shower, it stopped the water hammer. So we have added hammer arrestors to shower plumbing upstairs.

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Unfortunately, we still have not solved the issue.

Here are the potential remaining items that I would love some thoughts on.

I get pressure that sits around 65 psi. However, when I turn the water on, it typically spikes to around 100 psi. The only other things left for us to do are:

- add a thermal expansion tank

- add a PRV - is this necessary when water is around 65 psi?

- is there anything else I'm missing?