Gas boiler

Gizmo21

Has anyone any idea what this could be? We've had gas engineers visit regularly for the past 3 months, but because it doesn't do it when they're here, they have no idea what it is. It can happen at any time, it can happen when the central heating is on or just when the boiler is heating water up. I have my suspicions what it could be, but whenever I suggest it I'm told it can't be because because the boiler is only 4 years old. Surely that makes no difference whatsoever?!
https://youtu.be/9Y8unxrtvCU

Hasbeen

Perhaps posting in the Energy forum will get you more advice.

Rather than the Lpg, solid fuels and oil.

Gizmo21

Sorry, I wasnt sure which one to put it in as the "other fuels" confused me. I'll do that.