Can anyone help with this problem? Perhaps someone with an identical unit and similar problem can help resolve.

I have the following unit: MAKE: Burnham MODEL: Beckett
SERIAL #: 951030-4502 MODEL: “AFG” Series Oil Burner
BOILER #: 27112735 DOE HTG CAP MBG = 121
Steam Square Feet: 379 Steam MBH = 91 Water MBH = 105

I recently changed to a new local oil company. The new Tech performed an annual maintenance check-up. This is not a new unit so it’s been serviced by other local techs in the past. No problems were discovered but ever since his first maintenance check-up – the furnace has an additional muffled rumbling engine noise. Could the new Tech have done something that wasn't correct? Perhaps a new adjustment? The added sound is like truck engines driving by. No metal clanking just a louder but muffled engine sound. Instead of sounding like a quiet residential furnace – it sounds more like a commercial furnace with greater capacity. I’ve asked him to return several times to remove the engine rumbling sound but he has not been unable to detect a problem.

ANY SUGGESTIONS? PLEASE HELP!

William -HOMEOWNER