An update on the "hum". It has been humming quite a bit lately, and seems to happen in the daytime now, as well as the evenings. I do have an idea though. I have been narrowing down the times that it starts and stops. There is no specific pattern to the times, but I have noted that it usually stops when I turn the central heating off. It doesn't stop immediately, but within 2-5 minutes of the heating going off. This leads me to think that it is the central heating pump. Two points though........why does it hum for a little while after I turn the heating off and not stop immediately? And...why can I only hear the hum at a specific place in the whole of the house? I can only hear it in the sitting room, and then only when I stand in a specific place. Move two feet and it can't be heard. I can go to any other room in the house, and it can't be heard. It is really weird.....and it's driving me nuts! Does anyone think I may be on the right track? And can anyone explain those two queries?...Please?