Sounds like it could be the infamous subframe movement problem. The bolt holes in the subframe are a lot bigger than the bolt diameter, and therefore allows a small amount of movement. VW did come up with a toothed washer that digs into the subframe, but it doesn't solve it in the long term. The only way to fix it for good is with a subframe collar kit from TyrolSport, or I think ECS tuning do a similar kit also.
As well as sorting the noise for good, it also made the handling more consistent on mine, so it's well worth doing.
This issue also happens on other brands of car too, so it's not just VW. It's just a sloppy method of attaching the subframe in general.
Brake calipers/carriers can also creak at low speeds, so have a look over those whilst you're there.