VW Polo - new suspension arm clunk

More information on your car would be helpful. Such as mileage.

Here are the places which are a high probability for the clunk you describe:

• strut bearing/bushing area looseness and wear
• sway bar bushing (I don't know if the Polo has a sway bar)
• bushings on control arm
• linkages, such as sway bar linkages

The noise is not likely a loose brake caliper, but that should be easy enough to inspect with the wheel off. It's not a reliable indicator, but the clunk when braking kind of tilts the probability to the control arm bushings.