I just replaced my pressure regulator and am now experiencing similar sounds. But mine are more of a single ‘knock’ than a ‘rubbing’. Apparently it is caused by changes in pressure that cause the pipe to vibrate. You can try to reproduce it by flushing a toilet or turning on a faucet.
I’m not sure why it just started happening after replacing my pressure regulator. You’d think that a new working regulator would minimize it? Not sure why mine knock late at night when no one is turning on any water, perhaps it’s the contracting/expanding due to temperature changes? I think I’m gonna go through all the lines and make sure they’re secured at the proper increments so they don’t knock against the studs. Luckily all my pipes are exposed in the subfloor, so it should be easy.
