if it only shows up when he moved certain ways, it may be a shoulder blade deformity that he was born with? does it seem to be painful to him or hinder his movement with that arm? either way he probably could use a vet visit..
no it doesnt hinder his mobility in anyway. could this be because of a fall? there was an incident where he fell/jumped off my shoulder onto the ground, it was probably a 5 foot drop. he also fell from the top of his cage twice, but theres plenty of foliage in his cage.
Could be some form of abcess. Without a vet visit we're all guessing. I'd say he needs some tests run on that thing. You dont want to wait to long it will prob get bigger with time. When you do take him be sure you go to a reptile exp'd vet. You need someone that knows what they are doing with things like that. You dont want someone throwing shotgun treatments in an effort to possibly find a cure. In fact I'd send several pics to someone like Dr Greek or Dr Ivan Alfonso. Both those guys know their stuff and can assist your reg vet in a treatment program.