Do the burner flames go up and down in sync with the chuff chuff sound? It could be a loose cover or faulty flue/air duct. Potentially very dangerous to carry on using it. Best to shut it off and call a boiler engineer. What model of boiler by the way?
So why are you asking for help? If you want advice you have to be willing to supply information. Since you're not willing to even tell us what model boiler it is you can chuff off.
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