OP here--he eats Orijen "Whole Prey" kibble, and has been for past 2-3 years, so no change there. I occasionally give him a bit of dried chicken treat, but no recent change there either, and just a couple times a week.
The only new thing he's gotten is a bit of dried salmon treat, but honestly I think he was itching before I opened that bag.
I was also thinking fleas, but I haven't seen any, and he gets monthly flea treatments (Frontline and Sentinel).
Not sure what it could be--will take him to the vet if need be but had been hoping it was temporary...