So it warmed up from -40C to 0C this week (that's -40F to 32F for the folks in the US)...and what do you know - there's a pool of water bubbling up from the middle of the street! Definitely a leak somewhere in the city system and causing air/noise/pressure to travel up my copper service and bang in the house. Excavators coming later this week! :)

I'm still going change out my old valve for a new ball valve, but don't think I'll need the PRV/arrestor after the city's fix is done.