Not sure if this is the right forum or if it should be in "off topic". But anyway, if I pull out any more hair over this I'll be bald!!!! Does anyone know any gas men who would have any idea what the heck this noise is? Or has anyone had a boiler do this? It can do it when the central heating is on or just when it's heating the water up. We've had numerous gas men visit but because it never does it when they're here, they have no idea what it is and whatever I query, they say it can't be that I have my suspicions of what it could be, but I'm interested to see if anyone thinks the same.