Main Eco 28 Boiler - loud foghorn noises

Happyalways

I have a Main Eco 28 Boiler set up as a system boiler which has gotten really noisy over the last 8 months. When it fires up there is a long and very load "moan" like its struggling to suck something in. It then makes a loud humming noise as it runs. I’ve had it checked by British Gas and they also just did an annual inspection but the engineer just sort of brushed off the noise. He said boiler is working fine. However it’s so noisy I can hear it outside the house on the street.

The boiler is from 2012 and has a limescale filter installed which I clean regularly. British Gas said it is safe but I’m still concerned because they checked it as part of the annual check up and worried they didn’t consider the problem properly. Anyone experienced this issue, know what it could be? I have nightmares about the boiler exploding….

WIAWSNB

You can fix this by getting a proper GasSafe to look at it
No idea of the cause, but it can't be normal. Possibly a failing fan - worn bearings?
Could you take a short vid clip, and stick it on YouTube? 
I'd also message Main about it - they'll likely have a Facebook service too, so you can attach the clip.