My dog has a few really small lumps on the back of his ears what could they be?

They are any were on the back of his ears and they go away after a while.they are skin colour with a small orange dot on top. You can only see them when you separate the fur but if you run your hand over the ear you can feel them. If they are scratched they bleed and the orange tip can be taken of but a new one will appear. We first thought they were gr seeds but they definitely aren't. They keep coming up on his ears and i just want to be sure they are nothing bad. Does any one know what they could be?Also my dog is a male german coolie cross from the rspca he is 3 in october (2 and 5 months) and we have 2 chickens male and female , two rabbits male and female, birds in an avery , koalas kangaroos and foxes often come into our Garden. we live on one acre and he often goes in paddocks with long gr has contact with seed gr and goes to dog training. he also plays with out next door neighbors dog.