Driving out to see the Hulk at our local cinema yesterday, I had just achieved motorway cruising speed (about 60mph), when a louder than usual rattle became audible from the engine compartment. I pulled over to the hard shoulder, and got out to have a listen. The sound was coming from under the rocker cover, and was much more pronounced on acceleration. I haven't had a chance to have a look in there yet, but I'd welcome some estimates as to how serious this could be. There didn't seem to be any significant loss of power, and I was able to drive it back home, although I took things very easy because it was so loud.
Andrew
PS. In case anyone's wondering, we motorbiked out to the cinema after dropping the Land Rover off, and got to see the film.