Sounds normal to me too. I have one of those. He will turn 3 next month. He was the easiest baby on the planet - seriously low-maintenance. Happy all the time. He was so easy that we lulled ourselves into having a fifth child afterward.
He's still a very smiley guy, but he has his moments. He's been in a montessori toddler program all school year and does not participate in circle time. If I try to sing, even to the baby, he says "turn it off!!" (LOL ok I know my singing stinks but...) More recently, once in a while at school he will sing, but off to the side, not in the circle.
He came with me to his big brothers' birthday celebrations at their montessori K. For one, he was willing to sit in circle time though he wasn't pleased with the brief singing that occurred at one point. For the other one, the next day, they happened to be singing some random song about the month when we arrived, and he completely freaked out, huge enormous tantrum, wouldn't even enter the room (this was for one of his two possible teachers for next year when he starts preschool there - I don't think she wants him now LOL). This tantrum was so huge that it lasted till we got home and he had so lost all control of himself that he stripped down naked and tried to go outside (this was a couple months ago - it was cold!). I've seen some big tantrums in my time, but that one took the cake. Running upstairs, slamming doors, trying again to go outside naked...
Honestly I think it's a normal developmental phase. All three of his older sibs had issues at this age (two with SPD, and the one who didn't have SPD had head-banging tantrums at this age from frustration over not being able to speak). I'm just glad he's not as whiney as they were (are?).
Whenever we're at home, I try to let it burn itself out. I know, not possible in public.
I think it's not unusual to have these experiences even with three year olds. (as in, some kids don't have the terrible twos so much as the terrible threes.) So brace yourself
I too long for the return of my one compliant child. I had been tempted to sign him up for swim classes this summer, but they require separation - based on how he's been lately, I'm afraid to even try... he's now more aware of things that make him scared.
