There is a peculiar noise. IE its one of those very quiet intermittent
whirring noises that you can only hear when its quiet at night, and once you
know its there, you find it wakes you up.
The problem is that its seemingly everywhere and nowhere in that its no
louder wherever you go except in the upstairs front rooms.
My suspicion is that it is part of next doors central heating that is
somehow transmitting the sound through the building, but she can hear
nothing she says.
Any tricks other than asking her to turn it off and on again, which might
well not go down too well?
Do others have noises? Add to this of course that you don't it when normal
sounds are there in the day.
Brian

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