Boiler buzzing through surround sound

[Johnyhp]

I have a Vokera 20-80 RS Flowmatic and I have had surround sound for approx three years with no probs.Recently had work done on heating system and now when boiler fires for central heating I get a buzzing sound
coming through my TV speakers.
Not the end of the world, but annoying.
Sound only seems to last when gas jets are firing.There is no noise from the boiler itself and the boiler ,heating and hot water all seem to be working fine.
Does anyone have any idea what could be causing this?
Thanks
Johnyhp

 

[kevplumb]

supressor is paggered

 

[Johnyhp]

Any clues as to where the supressor is on this boiler?
I havent seen one listed on the parts diagram so I assume it must be part of somthing else ie PCB etc

Thanks

 

[nickso]

usually attached across the gas valve connections