Water pulsing in upstairs bathroom shower

Question

This only happens in the upstairs bath. City water, house Cir. 1921, copper pipes, older remodeled bath/shower, turn on shower to warm up, flush toilet, pulse begins (staccato not hammer). Turn on sink water, pulse stops, turn off, pulse continues, toilet tank fills and stops water flow, pulsing stops.

I can't remember when this started; just got used to it happening. My neighbor down the street has the same problem but worse pulsing.

Answer 1

indications are it is the pressure regulator

go outside and find it, then give it one turn clockwise

if that doesn't help, you might need to replace it