radiator noise travelling around the room

[dimi 229]

the boiler has just been checked over its fine but some rads clank especially in one room in which the noise travels round the room at about 4.ooam every day.The boiler man told me always to switch off the boiler before bleeding rads if not air is sucked in rather than being let out.
Please some helpful hints :

 

[BazThePipeman]

Please go to the main forum page and read the note about what info you need to supply when posting messages. Without knowing any info about your system its difficult to analyse.