Hello,
As soon as I turn the thermostat on, running water sounds coming out from pipe would last for about half a hour or so and then it disappears. It will recur after a while. It is extremely annoying at the middle of quiet night that wake everybody up. I am using Weil-McLain water Baseboard Radiators throughout my house. Please help.
Thanks.

Is possible you got some air in the lines and need purging, is it through out the house or in certain areas?

Yes. I also notice this happened after my plumber has flushed the system. I remember there was a lot of rusty water came out through a garden hose at that time.