I know, GBW, you said a lot of people asked if your kitty was spayed? Probably, because most cats will meow incessantly, when they are going into heat!!!!!
But, if they are meowing, just to meow, maybe you could try getting some of those Comfort Zone Diffusers, to help calm them down? Just a thought! I know they do not always help 100% of the time. My friend got some, and it helped only marginally. BUT, for my two kitties, it helped TREMENDOUSLY!!!!!! I mean, it is like night and day now, with the use of two diffusers here!! So, it may be worth your while to try one or two of them! I have one in the kitchen and one in the living room. Those are the 2 rooms they are in, the most. There is no scent from them, that humans can smell(although they look similar to those Glade Oil Plug-in things). Only the cats can smell them, and they emit a very comforting smell to them, which apparently is a similar scent to a nursing cat mommy!
Hope this helps!
P.S. They sell them in a lot of petstores. I went online, did a search and found them online, to be cheaper. Also Ebay sells them!