I agree with all the advice given. Let him crack on. He has to realise this mewling, whinnying etc is going to get him no where. Its the same thing when people say after they've ridden 'Oh, he wasn't great today but he knows his feed is in his box/its his field time/his friends are outside' sorry, but your horse is there to do his job, and he must learn this. If anything, when you are riding, keep him distracted as much as possible. Warm him up, don't do a whole length of a school without using a cirlce, a serpentine, a turn out of the corner, a transition or four!
Herd behaviour is normal, I completely agree, but these are working horses, and he may have to relearn that you pay his feed and stabling, so play nice ;)
Hope this helps!