There's a number of reasons why the strat would buzz.. But it's most commonly a floating earth or interference from monitors. If you want to get rid of it, you can get some of that gold foil that you get at plant nurseries, and put that into your electronics cavity.
2 articles on this issue:
http://www.soundonsound.com/sos/aug06/articles/guitartech_0806.htm (this article is AWESOME!)
http://www.soundonsound.com/sos/sep04/articles/qa0904-8.htm