chow here is an attempt. It is all very nicey nicey as we don't want the TA or school to dig in. Obviously I know very little about your case, but I hope this gives you a framework to amend to suit.
"Dear X
I am writing to offer some guidance and support to staff who are not familiar with Tourettes, or its close neighbour ASD-stims.
In my ds these stims are squeals which he cannot control.
For many pupils with Tourettes and stims, the uncontrollable noises are more likely to occur when the person is under stress.
And of course, one source of stress is becoming uncomfortable about the inconvenience that the noises cause to others.
Obviously, being reprimanded or isolated is going to be completely counter-productive. But even a frown, or sympathy to a fellow student for having to put up with the noise, or an off-the-cuff remark is likely to result in the noises increasing. And that of course makes it harder for the rest of the class to learn as well as the child with Tourettes/stims
I do understand that the instinct of any member of staff is to assume a child who looks like a mainstream child is making the noises for a mainsteam reason.
I also know staff just want the best for all their students and fortunately if we work together we should be able to make a good difference fairly simply to benefit the whole class.
Luckily it is relatively simple to put a system and training in place to remind staff to reverse the instinct to comment or reprimand, for a child with tourettes/ASD stims.
Your staff are clearly not the sort of people who would comment on a child with a wheelchair for the squeaks of the wheels on lino, let alone exclude them or reprimand them. So I am sure that when they understand that stims cannot be controlled, but can be reduced, they will be keen to help for everyone's benefit.
Could we discuss the structures that would work best for your school and some information sources that might assist?"