As Jocko says, it's normal to find a bit of movement in the joints, it certainly doesn't look excessive and I would be very surprised if that's the source of your knocking.
Much more likely to be a bad suspension joint, bush or top mount somewhere, droplinks are always the obvious place to start. Knocks can sometimes hard to diagnose, but anybody worth their salt should be able to find it.
I know you shouldn't be having to do this with a warranty, but get the car on a flat surface and rock it with the roof sills, you (or an assistant) might be able to hear something clicking. If you can replicate it that way, it's in the suspension somewhere. If you want to go further, the assistant can reach and grasp each joint tightly, or wedge a bar in to stop it moving - when the noise goes away, you have found the culprit.
Is it less noticeable in wet weather? Less/more noticeable on bends? How about low speed over road humps? Can you feel anything through the steering wheel or the floor? Is it a hard metallic rattly knock, or a softer thump noise?