Cat Scratching

I have a Maine Coon cat that has a problem that seems to get worse in the winter. Cat is 3 years old (around that) and will scratch behind his ear until it gets bloody. That seems to be the only place he does that. Doesnt have fleas or anything else we can see. Any ideas? We've has him since Dec 2002 (he was a stray that was dropped off on my friends porch) and has always been in great health. He is an outdoor cat (well, both in and out).

Thanks

Rich

Are you sure he doesn't have fleas? I was sure my cats didn't until my vet ran a flea comb over one and pulled out a live flea along with a bunch of flea dirt. Another possibility would be earmites. I would suggest a vet visit, as if he has fleas or earmites he will need medication from the vet to get rid of them and prevent future investations.