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Is he tame yet?
If he's still a bit nervous making sounds like clicking your fingers could cause him to freeze & appear not to have heard anything, ears down is usually a sign of being nervous or afraid too, unless they are unwell when the ears might be down.
Does he react to you normally otherwise, if you hold a treat for him does he respond & are his ears up?
It can be very hard to tell for sure if a ham is deaf but if they are then you just have to take extra care not to startle them, they will still pick up vibrations so will sense you rustling substrate for example so you can do that, avoid approaching from above or behind where they can't see you coming.