Worcester 34cdi noise coming from resonator intake and flue smell

[Tonyh1123]

Hi, I have a Worcester 34cdi boiler and it has started making a droning noise when it comes up to temperature or cycles. The sequence appears to be:
-Fan speeds up (purging?)
-Sparks, then lights (flame icon showing on display)
-Fan slows down
-Droning noise (like Jaws is coming, Daa-Daa, Daa-Daa)
The noise is coming from the resonator intake and when it makes the noise, it 'farts' gas from the intake that smells like flue gas.
Video of it is attached.

Thanks
Tony

 

[Tonyh1123]

dont know whats wrong with the video, ill try again here: