I keep hearing a noise in the house. It's like a humming sound or something trying to start. It's not constant but can go on for a good few seconds before stopping.
It seems to be getting louder - although DH can't hear it al all 
I don't think it's electrical as I've experimented turning various bits on and off.
We had the pressure balloon for the heating replaced recently. It's at 1 on the pressure gauge - is that too low or too high (three storey house)?
The cold tap has occasionally been making a noise when it is turned on.
Is it worth calling a plumber??