This is possibly a dim question, I never thought DS1 stimmed, however after reading Tony Attwood I realised that his monotonous whistle is a stim - he does it more and more if he is unsure about situations, bored etc etc. He has never really had a movement stim though.
DS2, who is due to be assessed for ASD in September, often if made to sit still (or if he gets excited) will start making a shriek noise and waving his hands in front of his face - always the same movement, or he gets pieces of paper and throws them in front of his face. Is this likely to be stimming?