Boiler "grunt" noise when turning on

[cs12345]

Hi there

First post so apologies if this is in the wrong section of the forum. I have an issue with my boiler making this low noise when the central heating fires up. Its best described as a "grunt"..

Can anyone advise what might be the issue - I live in a tenement flat and I am concerned that it may annoy neighbours.

 

[ShaunCorbs]

Need a gas safe engineer I’m sorry to say but common fault so shouldn’t be too bad