Would love some advice.
I recently remodeled our bathroom. Moved single shower across room to larger shower stall with 2 units. Wifes has showerhead and separate handheld...works of single lever for H/C, then goes to diverter for with shower or handheld.
Mine has just a separate single lever for showerhead alone.

Problem is we get a "thumping" in shower area when toilet finishes flushing, or sink faucets are turned off.
When I close cold water stops on shower valves, thumping goes away. after opening cold water stop, noise is still gone......but if I trun shower on/off, or flush a toilet or open close sink faucet, then noise comes back.

I've switched the cartridges 3 times. Does not fix problem. Have install water arrestor at toilet...did not fix.

I'm thinking the spool in cartridge is making the noise?? Should water arrestors be placed at valve on cold water side?? Or any other thoughts??
All plumbers and vender with showerheads are at a lose.

Really appreciate any help.