noisy combi boiler

I have a glow worm swift flow 100 boiler which is 8 years old. I recently moved a radiator after turning it all off and when I switched it back on there is a noise.. a sort of whirringWhining noise everytime the pump speeds up. Is this a result of the bearings on the pump being knackered, or is there some air in the system that i have to bleed out somehow.
The central heating and hot water are working fine, and I have tried bleeding the radiators which do not see m to have excessive air in them at all. The pressure remains constant on the dial.
Any clues on how to stop the noise?
Cheers
Tony
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It could be air. It could be the pump. It could be that you didn't flush the system after doing the pipework and some swarf has caught in the pump. Strainers before the pump are your friend for this.
Christian.
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