Conclusion from previous post.

I haven't told you what make of car I drive ... sorry, not going to tell. Anyhow.
"We don't service that many hard-top convertibles," the service supervisor admits to me after about ten days. "We're opening a conversation with national HQ to find out if they know something about this alarm problem that we don't know." No, there is no recall on this model or any such thing.

By this time I am quietly window-shopping for a different car. Not a convertible. No sun/moon/stars-roof. Just a car with a solid top with no window-roof in the top.
This takes a while. The dealers' inventory, in this make, invariably lack cars with plain solid inflexible tops/roofs. The inventory is instead, without exception, tricked out in sun/moon/stars-roofs. So I head toward used cars and older models of the same make, as this make of car suits me very well when there isn't a screaming-meemies beeper alarm going off.

Long story a tiny bit shorter:
National HQ, contacted some ten days after I handed over the screaming automobile, knew what was amiss. There was a screw loose next to one of the sensors in the electronics in one of the rear pillars. Tighten said screw, and voila, no more screaming.
By this time I had taken my rental car to a used-car dealer on the far side of my home county, and test-driven a car of the same make which had a solid plain un-alarmed top/roof.

As soon as the bill was paid for the service, and the convertible was back in my possession, I drove straight to the used-car dealer and traded in the hard-top convertible for the dear old sedan with an ordinary roof.

Yes, it is an OLD used car so there will be problems down the road.
But for now it is rolling along nicely, and the roof sits there silently as a roof ought to do. No more convertibles for me.
It even has less electronics than my convertible had.
And it's still my preferred make of car. Exhale. Thanks for listening.