A familiar question I would guess! When the boiler goes on at 5.30am I occassionally wake to hear a noise akin to to a soft "tap-tap" or creaking sound from the central heating system in my bedroom (on the first floor). Whilst half in the land of nod this morning and awoken thus I had a look around the house (I have a cold water tank, a one-year-old boiler (flushed too when installed) and there are seven radiators on two floors) and none of the noises were coming from the radiators themselves (which have all been bled of late) but appeared to be in the pipes feeding the radiators. Any clues?