Well that is the first step to find out what is making him scratch. Sometimes it can be the food regardless of the corn/wheat/grain because they can also be allergic to fish, chicken and meat or any of the other ingred in the food. it can also be enviro such as fresh cut grass, pollen etc....also it could be the shampoo you use or how often you do a bath, any treats that you may feed. It could be what you wash the pups bedding in, something you use to clean your home. The list is endless sometimes. The first thing to check for is of course fleas, earmites, ticks on the body, did you just put a collar on that the pup is not use to??? Try to think of anything that changed right prior to the scratching on set....