Help! Our boiler (Ideal wall mounted) is making a loud "whining" noise which starts shortly after it comes on and continues on and off during the day. The noise can also be heard in the tank cupboard in the bathroom upstairs. We have had the fan replaced but it hasn't stopped the problem. We have also bled all the radiators. Any ideas what it could be and what we can do about it? It has been doing it for several weeks now.