Mazda engineers understand that EVERYTHING expands when heated, so when they designed the 3.0L, they wanted a particular valve clearance during operation, and that required some "weirdness" with the spacing. This "weirdness" in some engines (manufacturing process is never perfect) causes the motor (usually right bank especially) to do a little ticking/clicking when the motor is cold. Don't worry about it unless the motor is really loud (opinions being rational) One thing to be aware of, however, is the non metal timing belt. When it streches like it does, the valve timing changes a little. If that thing breaks, the motor can be severely damamged. Definitely  have your timing belt changed every 60,000 like I beleive the manual states.
Darnell