Thanks for your comments. I'm inclined to believe it is a territorial thing as well. They are not being fed together now and that seems to work okay. They are both fussed over equally and they seem to be more content. Eating furiously now seems to have quietened down considerably.
I agree with AnneBrooke. Most likely being territorial, with a combination of stress over all the changes and new environment. I would give him extra TLC until he becomes used to everything. Give both cats treats and love when they are together so they learn to see each other as a positive thing.
It could be the competition, stimulating his territorialism over food, for sure. If he has been exposed to prey and / or fleas, it could also be a tapeworm. (Ya gotta eat more when eating for two.) Possibly take a stool sample to the vet.