Focus 2008 'clunking'

[Elroy Blue]

We've got a manual 2008 1.6 petrol focus that we've had for five years. Well looked after and fully serviced. In the last couple of weeks it's started making a slight clunking/clicking noise when the car drives between 10-15mph. It only does it when first starting off on a journey.
Google has brought up 'ABS self testing'. While the symptoms seem to support this, it's odd it's never done it before.
Is it likely to be the ABS or something that needs looking at quickly?