Two of ours have a plastic dash rattle, though it's more of a plastic knocking.
One sounds worse than the other and on the Lounge you can shut it up by pressing against the head unit slightly, the Pop is far worse and carries around the car quite badly, but that one doesn't respond to the same push or the head unit.
It's not a major issue as they both shut up once warm air comes out of the vents, so I presume it's a heater pipe, when cold they might be catching the back of the head unit or something around there, but once warm it might have expanded and jammed it's self against something.
My 4x4 TA doesn't seem affected, or maybe it is, but the engine Grrrr drowns it out!
I've had a look up under the dash, but you can see nowt of the top part of the dash.
Keep meaning to remove the head unit and have a look, but the weather puts me off fiddling at the moment.