Have a strange rattling/scratchy noise coming from the back of my engine though doesn't seem to be coming from the engine itself (Volkswagen V5). Could this be the catalyst on the way out?
It might be as simple as a baffle in the exhaust has worked loose (which you can't do a great deal about) or a heat deflector around the catalyst could have worked loose. An enterprising 'under the arches' garage may be able to fix (bodge) the latter.