Inappropriate shouting

[nikos]

Ds (3.5) is currently being looked at for ASD. But at his last assessment they felt he was progressing so quickly that it might not be ASD but a language delay.
He has now settled into nursery really well, after about 6 months of aggressive behaviour, and will sit nicely with the other children in close proximity for snack time and story time.
What we still really have problems with is shouting at staff when he arrives . They only have to say good morning in a nice friendly voice and he shouts at them. He also will not sit with the others for register. But after this time (about 15 minutes into the day) he settles and plays well.
One theory I have is that the lead worker often chats to the children at register time and that he finds that threatening in terms of processing the language. But to be honest I'm at a bit of a loss to explain it. He can be in a very good mood before we go in and then just turn.
Does anyone have any ideas about what he may be thinking or ways to get him to sit nicely for register?

DS didn't start toilet training at all until he was 3.5, took quite a few months to get up to the no nappies outside house/nursery stage.

Toilet training was the first time DS2 ever got upset about anything, it took until he was 3.5 to get the hang of poos, to put that in context his two brothers were clean and dry, night and day by just past two (one of the few things i have ever been able to boast about with my RL friends!). My mother in law used to joke that she thought DH was going to go to school in nappies and he shares a lot of traits with DS2. DH also ended up with a phobia about public toilets(in fact any toilet not at home) that really restricted his life and wasn't sorted out(using CBT)until he was 35! For a while my life was dominated by toilets, glad thats over now.