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I think best safest way to test is with the rear tire off ground. Whichever way accomplished. If there is a will there is a way - I use a small motorcycle jack placed against the folded center stand. So, technically the bike is put on the center stand, and done with one hand! L0L 0ther than that, I remove the seat (my long legs still too short) and drive the bike on a piece wood - this way I manage putting the bike on the center stand with my left foot. I thought it will be easier with the handle but still too much to risk twisting my knee again and falling over.

Just seems like the obvious place to start given all the parts involved, that will certainly rattle to some degree if there's any slack in the adjustment.

Even with the clutch adjusted incorrectly it still should NOT make any form of Metallic Rattle with the lever pulled in.............

Pete F
UK

I purchased a used complete clutch some months ago. One of the steel plates was there but cracked, split into halves. Hard to really say without a video, but this could be one possibility.

This is the problem with on-line diagnosing. What constitutes a "rattle? What's the difference between a "normal" rattle and a "metallic" rattle ? It's all speculative and dependant on ones ear. I'm sure if you asked 10 people to describe a "rattling sound" you'd get 5 different answers. Keys on a ring, two wrench's banging together or a couple of tags on your dogs collar. They all "rattle" !
An audio of the "rattle" as stan suggested might be helpful but I've tried many times to get a sound-bite of various such noises and it's difficult at best to get the recording device to isolate it, or to disseminate the various other noises from the one you're trying to identify.
Further to the "adjustment" idea: If the adjuster was too tight, the clutch-plates would separate more then usual when the lever is pulled and.......would that not allow the plates to "rattle" more then "normal' ? When the lever is pulled in, the clutch plates are basically 'floating" ........aren't they ?
A mechanics stethoscope may narrow the field. The mystery sound may not necessarily be coming from the clutch assembly but merely be manifesting there due to simple harmonics.
As suggested: Pull the clutch cover and look for "the obvious" because at this juncture - anything is possible !