Cat won't shut up!!!!!

We adopted an alleykitten back in September, and things seemed good, up until a month ago. Allegedly mom had a litter of kittens, and she along with the rest were ran over. This little guy was living in a dumpster. He adjusted quickly, and seemed well on his way to being a happy house cat. We had already had an appointment made to get him neuteted, when he started meowing. CONSTANTLY.

Before this, he would meow, but only for good reason. He either wanted food, water, picked up (not a lap cat, loves being held.) We even got to the point where we joked that we could identify his different sounds and what they meant.

He started meowing more than normal, and we thought this was teenage hormones, and that the already scheduled neutering would help.

After he got home and recovered, he started meowing again. More. And more often. And louder. He does not seem to be in pain. He runs and jumps and plays and does all the things a healthy juvenile male would do. He eats well, uses litter box, and seems physically fine.

Before, he would usually go to what he wanted, or lead us there. (I.e. empty food bowl, too full litter box, etc.) Now he just paces the house screaming every 10 minutes. Like right now he's doing it. If we ignore him, he just gets louder and louder. To the point im afraid the neighbors will complain (we live in apartment).

We've tried playing, he gets bored in 2 min and starts screaming again. He usually loves being picked up, but when he's like this, he wants down after 30 seconds. We've made sure he has everything he needs, but nothing shuts him up. We're at out wits end here.

Any ideas are very welcome.

Thanks!