NOISE FROM BOILER?

NOISE FROM MY NEIGHBOURS CENTRAL HEATING FLUE DRIVES US MAD. THEY HAVE AN ARISTON COMBI BOILER - IT FIRES UP EVERY MINUTE THEN GOES OFF FOR A MINUTE - ALL DAY - NEVER CUTS OFF. IT EMITS A HIGH PITCHED NOISE THAT WE HEAR ALL THROUGH THE BACK OF OUR HOUSE. THEY SAY THEY CANNOT AFFORD TO REPLACE IT - WHICH I UNDERSTAND. ENGINEERS HAVE REPLACED FLUE BUT TO NO AVAIL. CAN THE OUTSIDE PART OF THE FLUE BE EXTENDED MAYBE UP - TO DISSIPATE THE NOISE? THAT WOULDNT BE TOO EXPENSIVE? ANYONE HAVE ANY IDEAS?