My DS9 has tourettes and has done some of these behaviors as well, for him they are identified tics. Tics are common for many children espcially in this age range. They are frequently seen in boys. It doesn't mean that he is ticcing but it is a possiblity. It also doesn't mean a medical diagnosis b/c tics do happen w/ many kids. If that is the case they will decrease in the future as he develops other stratagies for sensory issue.
For the fidgeting in his seat there is a rubber type thing that he can sit on that lets him squirm unobtrusively. he loves it. It came from the OT in his building. Many kids do well sitting on a balance ball. it takes focus to remain upright. It strengthens the central core. It also allows for mild movement. My son is also a hummer. He isn't even aware of doing it. He teacher quietly ask him to turn down the volume. That has worked well for him.
