Serg has posted some great information about fret buzz on his site Guitar Daily. He goes into perfect detail on the causes of fret buzz and how they can be rectified.

To sum up his posts causes could be:

1. Old strings
2. New strings that have not settled
3. Action is too low
4. Bent or warped neck
5. Inconsistent fret heights

If you are experiencing buzzing on your frets I suggest you head over and read his posts.
Top Reasons For Guitar Fret buzz
Fret Buzz – Guitar Action
Fret buzz – low and high frets
and Fret Buzz: Neck Relief, Bow And Back Bow at Guitar Daily.

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3. Ernie Ball Music Man John Petrucci Signature Guitar
4. Getting my Guitar Professionally Setup