Check the rim tape. My wife bought a new bike with Aksium wheels last year. She had a couple of flats. I never found anything in the tires and the spoke heads were covered. I finally took a close look at the rim tape and found that the tape was folded over on itself. I removed the rim tape and re-installed it. Then I heated the rim tape with a heat gun and burnished it with a metal tire lever. Not a single flat since then.
Next time she has a flat, I'll replace it with Velox rim tape.