The Deutz in my Mecalac has recently occasionally started making this annoying rattle at high rpm. As soon as I idle down it stops, and sometimes it stops on its own. I can't pinpoint where it's coming from. Has anyone else experienced this with a Deutz?
I would look at all your exhaust guarding. Had many rattles on a HD that ultimately came down to a loose exhaust bracket. Looks like your belt tensioner is on its way out also.
I'm trying to visualize a Deutz in a Harley Is it turboed and intercooled? The belt is manually tensioned by the alternator, and it's tight when the engine is off.
Follow up: the rattle eventually went away on it's own. I assume it was something with the exhaust shielding (maybe a pebble got down inside it, or if it was a crack maybe it cracked enough more that it doesn't rattle). If I ever have need to remove the exhaust maybe I'll find the cause.