My son says things in interesting ways, also 11, also dx'd ADHD, and dx'd at 8. Was he dx'd by the pediatrician or psychiatrist? If he has a pdoc call them. If not call his pediatrician and ask for an immediate referral to a child psychiatrist. There is the option of county health if in the US. I'm really hoping your seeing a pdoc. If he's not in therapy, get him to one ASAP. Understand his mind is currently completely torching him. So try to make him feel that what he is talking about is completely normal, fear or uncomfortable-ness from your side will make him feel he's bad. Please talk to his dr alone about this Preferably while he's in school so that it doesn't cause him distress or paranoia.

As him exactly what they say. Give him short positive statments to 'yell' back at them. I wouldn't worry that they're from Satan, the scariest thing a child can think of. Please remind him that you think he's the bravest kid ever and you are so proud of him. Get him noise canceling head phones to block out outside sounds and put songs that go to a deep base beat. Ask him to come tell on it when it get annoying. Keep track of this. If it is bothering him let him use the music

If he has an IEP ask for him to have noise cancelling headphones for tests. Also tell his teacher that he may be preoccupied because there's been some "family issue" or if s/he know's he's on meds tell her he's going through med changes. Don't be afraid to ask about it. Right now, he needs you as his stability and 'kids gloves'. So any little special thing you can think of to do for him to make him safe, secure, and loved is good. Even cuddling in bed and reading a book before bed.

Just try your best to make it as comfortable for him to talk about it as possible. Also stimulants can cause issues for kids that have co-morbid issues.