Metallic knocking noises from the front suspension can usually be narrowed down to a few components, most likely a failing anti-roll bar drop link.
However, the noise you describe sounds more like something loose - it might be worth having a look under the front bumper in particular, to make sure none of the plastic undertray components are loose. Get hold of each part in turn and give it a wiggle, nothing should flap about. The clips with hold these in can break with age and/or drop out.
The circumstances when the noise appears might help you diagnose. Is it particularly on road bumps or potholes? Does it stop when braking?