It is likely that there are air bubbles in your heating system.
Bleed the air from the system by opening the bleed valves located on the noisiest or highest radiators in your setup (for example, in the upstairs bedrooms).
Use a cloth and proceed radiator by radiator. When you open the valve, air should escape. Use the cloth to protect the surroundings from any splashes. As soon as the heating water starts to come out, close the valve.
Be careful not to burn yourself: first, turn off your heating system and wait for your radiators to cool down before opening the bleed valves.
After this operation, the heating pressure may become too low: then, add water to the heating system using the filling valve (valve connecting the domestic water system to the heating circuit). Make sure not to exceed 1.5 bar.
If the heating system has been properly bled but the noise persists, contact your installer.
