EDIT: I've found the problem that was causing the game to rumble for some people.
How to Fix:
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1) If you haven't downloaded the story yet, download the story again (when I have uploaded the new link)
2) If you already have the story, the easiest way to fix it, is to reinstall the story again from the new download link.
Alternatively, you can go into [An Unexpected Arrival/maps/outside2.hps] in Notepad, and search for the line:
MovePlayerHeadPos(0, 0, 0, 0.7f, 0);
Replace this line with:
MovePlayerHeadPos(0, 0, 0, 0.7f, 0.1f);
Then save the file and open up Amnesia.
You will need to restart the entire custom story for this to affect an existing save. Sorry for any trouble caused.