One of the pumps, while not noisier than the other one when I'm standing next to them, creates a sound all over the house (even in the other zone). It is a low drdrdrdrdr sound like a cheap motor scooter in the distance.
It's a B&G "Little Red" pump, 1/20 hp, for heating maybe 400 sq ft (a newer addition). It appears to work OK (delivers heat). It has been lubricated.
Is it the pump, or something in its connection to the rest of the system?
If the pump, are these pumps by any chance "hot-swappable" (i.e. chageable without draining the system)? It seems to have one piece inline with the water, and the rest of the pump is mounted onto that piece from the side, but I don't know if it can be disassembled at that point.
Note, again, that the pump isn't particularly noisy when I am standing next to it. I don't know if that means anything.