My son (5) has recently started a thing where he will sort of “freeze” his upper torso muscles into a rigid pose, clenching his fist as he does so and making a humming noise. There’s no pattern to when it occurs other than it tends to be when he is not “busy”. Definitely not when he is anxious or stressed, more so when he’s happy but unoccupied or verging on bored. We’ve suspected ADHD for some time but this is a new development. Does it sound like a tic?