Glowworm Micron 60ff whining!!?

I have the above boiler which has started to whine at various times, whether the ch and/or dhw is on, and it is enough to wake us in the morning. The noise is definately coming from the boiler not the pump. I first thought it might be fan bearings but then realised that the noise alters in tone dependant on the setting of the pump. Highest setting highest noise. Any suggestions would be appreciated.