I have an Alpha 280e. When first turned on after about 10 mins it emits a loud continuous whining. This lasts for 2-3 mins then stops. It only happens when CH is on, not DHW. The expanssion vessel was recharged last year, and the sound seems to be coming from that area, could it be linked as it only happens when the boiler is first running, and so as the pressure in the system increases. Any help would be greatly appreciated.