Cocks can crow sitting down if they have a mind to, particularly Orpingtons.
I would check his throat Irenemcc. What you are looking for are cream coloured cankers, which apart from being in the throat will be in the airways. He would be carrying the TG parasite in that case and it has flared up due to immunity depression from the stress of the move. Unfortunately that would mean he has infected the hens, so hopefully that's not the problem. It can be treated though.
Aside from that I don't know, although a quiet cockerel is much sought after chicken usually.