I had a very annoying rattle coming from my dashboard on my T5.1 Kombi. Drove me nuts and the solution was really simple once I found out what it was. I took the dash apart hunting for the problem, radio out, glove box out, everything I could to try and find the rattle. Had nothing to do with the dashboard but sounded like it was coming from the centre of the dashboard. When driving it would rattle and what gave it away was the rattle happened when the engine was turned off and you shut the drivers door hard. In the skuttle tray under the windscreen, where the wiper motor is, in the centre there is a little metal box bolted to the underside of the dash. This box has some wires going into it at the back but just dangles there. After some research it turns out that this is the Alarm Siren which is housed in a metal enclosure. It was this box that was vibrating and making the blasted rattling sound. All I did was put in two extra long screwdrivers from each side and bend it more forward. That completely stopped the rattling sound. My neighbour has the same van and his siren box was further forward than mine (identical van) but both boxes move and vibrate when pushed with a screwdriver.
If you are investigating an annoying rattling noise then please save yourself time and effort and check out the alarm siren box in the skuttle tray. Buy yourself two extra long and thin screwdrivers, mine were 10" long, which will fit in between the vent slots, and carefully lever the box forward. It's a stupid design to have this mounted the way it is and being a metal box. It does have some foam pads on it but they did not stop it rattling. Open your bonnet and get someone to close the drivers door firmly while listening in the centre. If you hear the rattle then you know what to do.
Hope this helps someone and saves you going through the investigation process