Very noisey old glowworm ?

My Glow-worm fuelsaver MK2 60br is very noisey and vibrates the pipework so much it has become unuseable. I've had it to bits and can find nothing obviously wrong. Both the gas valve and the thermostat are fairly new. I think I may have a tiny leak in the exchanger which grows as the the boiler fires up causing the racket. I'm only guessing as there are no external signs of a leak. The pump, 3 way valve and cylinder are also fairly new.