I've got a new boiler installed with a 70-year old gravity system. This has a Taco 007-series pump for circulation. Everything is hard-plumbed together with galvanized pipe.
I've noticed that sometimes the pump makes the house hum. Really odd as it'll be noticable in some places but not other. Also it'll get the regular water going too sometimes. Really weird.
The pump seems to be running smoothly as it doesn't shake and it isn't loud by itself.
I've done some searching and can't find any products designed to help with this.