The easiest way to verify the noise is due to a particular injector or cylinder is to loosen the tube nut on top of each injector, one at a time, while idling. I recall that is a 17 mm wrench. You normally don't need to secure the injector since it is in much tighter. Loosen just enough so you see fuel dribbling out. That will disable that injector. If the noise goes away, it was due to that injector or cylinder. It will also help sweep any trapped air bubbles out of the high-pressure tubing.

My 1985 300D had a strange knocking or rattling sound around 2006 when driving 30 mph, about 5 years after I bought it. I pulled over, popped the hood, and the noise went away. It sounded like something was rattling around inside the engine. Maybe a year later, it happened again and a bit louder. I didn't make it home as the engine got weaker and died when I lifted the pedal when rolling down a hill. Couldn't even turn the engine over after that. Towed it home and pulled off the head. Something had beat up the #1 cylinder, leaving round depressions a few places in the top of the piston, like a small round bearing. I first suspected a turbo-pump bearing, but it has only solid bronze bushings. No idea what that was or how it got into the cylinder. I found several pistons with chunks of aluminum missing around the ring grooves and some cylinder walls scored. That was at 330K miles, and explained the low compression (~250 psig) and needing a block heater to start on <45 F mornings. I swapped in a used engine which had perfect compression.

I hope your fast-working mechanic wasn't so erratic to drop something into the engine while the injectors were off, but would have to be small to make it thru the pre-chamber holes. If you pull out the injectors, fish around in there with a small magnet for steel parts, plus look close with a good light or USB endoscope. As I recall, a 1985 engine has a straight view down to the glowplugs, whereas earlier engines have a neck which obscures the view, but maybe vice-versa. Sometimes the end of a glow-plug breaks off to rattle around in the pre-chamber.

Marrakech sounds exotic, but perhaps just residue from the Beatles days. More likely a poor-man's version of Southern CA, with more history.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans