Constant clicking from Promax HE

I moved into a brand new house just before Xmas, which was completed in June. The Potterton boiler that was installed has now developed an annoying habit of clicking every second or every few seconds (depending on how high the gas is) until I switch it off. I suspect this may be something to do with expanding & contracting metal ... it's been like it for about a week now (started after 2-3 days of use). Should I be worried or will it settle down after a month or two ??

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