woodymogs - When you say you turn the boiler off… Do you mean the machine off (brew boiler) or just the steam boiler off (eco mode)?
As you can see there’s a 4way connector there: Water from the expansion valve and safety valve join there and end up in the tank; one of the ends is just plugged to the end of the steam wand.
So… If when you turn the steam boiler off the noise stops… Then it’s likely you have a problem with the safety valve.
How old is the machine? If it’s still under warranty, contact your reseller.
