Graphics card buzzing noise in games

Last week, i picked up a macpro 2,1 (22g ram , nvidia 7300 gt 256mb ,2x3 ghz quad core intel xeon ) . While launching Minecaft , i noticed that when i crated a world , my nvidia geforce 7300 gt starting buzzing like a dirty fan spinning slowly hitting a piece of plastic. This also happen when the screensaver activetes . When i activate fast render in minecraft , the noise instently became faster , when i am looking in differents ways on minecraft , the noise become fatser or slower . I cleaned all the fans and the graphics card but the noise is still anoying me even in windows 7 (bootcamp)