Our home heating system is one which uses the main water system and fans to heat up the water and blow out hot air through vents. Can't remember what it's called... Often there is a high pitched whistling noise coming from the main water line when the heater is running. We noticed that when we use any of the house faucets we also get that noise. It's not consistent and comes and goes. What will help the noise go away is by turning on an alternate fauce in the house, flushing a toilet or even turing off the heater. We installed a new PRV over the summer to resolve a "ticking" sound in the pipes. The ticking diminished somewhat but only went away when the weather cooled down. Could this all be related? We have no loss of hot water and the heater, besides the whistling noise, is working as per usual. Any ideas? Thanks for any help you may offer.