Modern Vespa

A few days ago, I contacted a highly respected Modern member for advice regarding a screeching noise. (open video link]
https://www.youtube.com/@ricricestudios469
We agreed to share this on this forum to get a few of you on board to think this out.
After a few emails, it was decided to inspect the clutch area since the noise changed in decimals when engaging the lever. Moving on, I did notice the castle nut seemed to be moving freely. I'm guessing an eighth of an inch movement, but loose. It was tightened and proceeded to restart the motor. I should mention that the motor started within the first kickstart pump before tightening the clutch. Now, it won't turn over as freely as before resulting in a no idle. It feels like resistance to the crank while pumping the Kickstarter. Scoots in neutral and plenty of fuel. Could the nut tightening have caused this?

You have oil in the gearbox? Bad bearing?

Yes, oil is in the gearbox and the motor was rebuilt on the workbench 2 weeks earlier with new bearings.
It ran perfectly before the teardown. The screeching started after I was tunning the carburetor and making cable adjustments.

Is there a needle bearing on the FW side on the older engines?.... If so, that's it, had it happen on PX engine, needs lubrication on start up.

Maybe an issue between plunger and pressure plate?

Or an issue with main bearings or big end bearing on crank.. . .which reminds me i had a crank that sounds just like this in an original Allstate. replaced the crank and the noise went away.

I appreciate the responses, Thanks!
This motor was running for 2 weeks on a test stand before the decision to reinstall. Then after connecting and adjusting all the required cables, the screeching showed up. It started to make a screeching noise while in neutral and changed slightly when applying the clutch lever. As noted in my prior comments, the castle nut was loose and I decided to tighten it no more than a tab clockwise.

Stuarttiaien...Yes, the FW side needle bearing is new and should be well-lubricated.

GickSpeed... Originally, Only the piston was replaced but the crank did not show any ware or was deemed to be replaced. It's my gut feeling that the crank is not the issue because it ran off and on for two weeks totaling 8 hours on the engine stand. The plunger on the pressure plate has free motion and shows no ware.

It has started freely with one attempt and it hasn't shown any life since the tightening of the castle nut. I cleaned the plug last night thinking it was a spark issue to no avail. No one has referred to the tightening of the nut. I only wish it would start, so to see if the screeching was eliminated.

My brain exploded just before bedtime!

Fan rubbing? Have you tried it with the fan cover off?

Noise go away when you squeeze the clutch and rev?

If it happens in gear too, it's definitely crank top end. If it goes away in gear it's gearbox/lower end.

UPDATE ;
I did not mention it, but who would; the air box cover was reinstalled before the scooter had not wanted to start. Well, I removed the cover to inspect the cables this morning, kicked it over and it ran with no nightmarish screeching noises. Tested further by engaging the clutch, again, "NO Noises!" I'm ready to ride without a dust cover or at least determine why that happened.

The amount of confidence and courage this forum leaves me is simply outstanding!

I should have added that tightening the castle nut (in Greasy125s and my opinion) had eliminated the screeching noise for future members.