What is wrong with our Worcester Bosch Greenstar CDi Conventional?

We have a Worcester Bosch boiler installed 5 years ago. It has been working fine and been serviced up until this last month. After switching off in the morning, we have been experiencing an intermintent dragging/grating type of noise which at first was only for a few times. It does not happen every morning, but this morning the noise went on for 45 times after the boiler closed down. It appears to be lounder in the loft and the area is over a bedroom with radiater. Would be grateful for any suggestions for what could be wrong and could we fix it ourselves? Thank you.