Assuming you have the same VW style latches as most, and assuming they aren't just a bad part out of the box, here is some info:
These latches are designed to rotate past the point of latching and then spring back against the internal "stop". This only works if it has enough tension against the rubber seal. If it is not tight against the rubber seal, or not touching the rubber seal, then it has no outward pressure and will rattle like mad. If the door is properly adjusted or at max adjustment, then the fix is to either use a thicker bulb seal or to stiffen the bulb seal or add a 2nd rubber stop to add the required tension. One inside tip is that if you cannot get a larger seal, you can put a small slice int he rubber bulb and slip in a greased piece of rubber hose to make it stiffer. Just close the door and look far a few spots where it is close but not compressed and add the insert at those locations. You can leave the slice int heseal bulb or you can close it up with a dab of super glue.