usually loose valve adjustment makes a ticking sound obviously at the same rhythm as the engine rpms. although slightly loose valves are only annoying to the ears. i would not put off the adjuistment too long. it is a simple procedure if you do it your self. i hate paying through the nose at a dealer for something like that. as for the frequency, i have 2 03 ranchers that i have never touched the valves on and an 05 foreman that started getting noisy after about 10 hours. just goes to show there are no rules set in stone.