There's no noise when running water from the taps, and the Megaflo is 10 feet away and definitely not the source of the noise. The noise is coming from left of the boiler, where the expansion vessel, pump, and filter are located.
Has anyone ever heard this noise coming from a sealed central heating system? See -
The noise reminds me of air escaping from the neck of a balloon. It happens almost daily, for a minute or so, normally while the hot water (Megaflo) is on (heating is off as its summer). I can partly stop the...