Modern Vespa

When I put the scooter up on the center stand, I hear a loud clunk every time. I get the same clunk when I take it off the center stand sometimes. If I don't get the loud clunk immediately after letting it down, I'll hear it when I ride and go over the first bump. Any more bumps after that don't elicit the clunk.

I checked all the nuts and bolts at the suspension points and they are tight. For the life of me, I can't tell where the noise is coming from. Scooter starts, runs and rides nicely. 2019 GTS has 15,500 miles on it.

I can't find any past cases when I Google the problem. Anyone ever have this happen to them and if so, what did you do to fix it?

Without seeing a photo I can't say anything for sure.
Check the center stand's springs if they are rusty or in bad condition then change them. Lubricate the Center stand also helps.

Center stand springs look fine. I have not greased the center stand bolt as I really don't think that's the issue. The stand does go up and down very easily.

Could be the the swing arm springs. On the transmission side, near the silent block there are springs which are part of the swing arm. Also check the silent block.

Would you know how that spring and silent block work? I strongly suspect the clunk is coming from that area. I've looked at pictures and the scooter (as much as you can see without taking it apart) and I don't quite understand how the suspension set-up on the front of the engine works?

Remove the seat bucket and drop it off the stand with seat open while standing next to the bike and investigating. Might help to get an assistant.

I did that and couldn't tell other than the clunk seems to come from the front of the engine.

The rubber end-stop has broken off the centre stand. This can be quite serious if not remedied, as the steel stand can wear away the bottom of the transmission case or oil sump.

The rubber end stop on the centre stand is o.k. as that was the first thing I checked.

Maybe the battery is moving around?

Battery is tight in its compartment.

I have the feeling if the clunk is a problem, it's a very rare one. I could only find one other mention of it on the internet with no solution to it.

I do rack up the miles on the scooter so if it is a problem, more symptoms will become evident as times goes by. Like I said, the scooter rides nicely with nothing else wrong.

If it makes the loud clunk every time you put it on the centre stand, why don't you, with the help of another person do lie down on the floor next to the Vespa and have a visual of when the centre stand comes off. That seem a pretty simple solution, and it may save you a lot of trouble.. If the clunk is a metal sound, I wouldn't use the Vespa until I'm 100% positive of where the sound come from.. IMO...

If not the rubber end stop then check the silent blocks. One big one, two small ones. A PITA to replace, but doable at home with some swearing.