I had this on the my 1999 Rover 400 diesel and my 05 zs180 is rattling away now. I had to remove the door card on the 400 to see what was going on - can't remember exactly where, but there was a loose nut connecting glass or sliding mechanism - tightened it up (as I recall the window had to be raised/lowered in to the right position to get access to the nut) and it didn't rattle again in the 130,000 miles I kept it.
Removing the plastic triangle inside the wing mirror.
Removing two screws on the pull handle.
Remove the screw on the door release handle - this need to be slid (can't remember if its forward or back - don't just pull or you'll break it) before it comes part way out when you can see a little retaining clip which needs to be unhooked before you can completely remove the handle.
Prise off and 'unpop' the popper fixings around the side and bottom of the door card.
It should now lift up and off.
It's a bit of a fiddle to slide it back down (have the window open for this) but once it is, it's just tapping the poppers back on and putting the handle, clip and screws back in.
Take it easy, be carefull and 15 minutes easy to remove even if you're clumsy, and a bit longer to replace.