Ghost in cupboard?

Alpha 24eco combi Central Heating System. Last week before going to bed I turned the Thermostate down in the living room as usual. As I left the living room and walked into the hall I could hear a buzzing noise which I located as coming from our Alpha Combi heater upstairs in the old airing cupboard. I turned setting to 'off after 12.00 pm' though I usually keep it on all night, it has to be very cold to click on. All has been quite until this afternoon. When walking past the boiler cupboard you can hear a noise like a whine or a ghost singing. Its been like it none stop. We have not had our boiler serviced for about 2 years. That was when the heating packed up and the diaphragm was replaced. We have a Electric carbon detector. What do you think it is. My worry is it's going to stop working, but do not want to pay out for a silly thing.