I have a core i3 in a Silverstone GB04 case with a Scythe SCSK-1100 Shuriken heat sink/fan. I use SpeedFan to vary the speed of the case and CPU fans. It's a bit of a trade off between heat and noise, but at "idle" (that is nothing going on but XBMC running) the CPU temp is around 46C, the CPU fan runs about 1100RPM, and the three case fans run about 700RPM. With those settings, a cabinet with a somewhat open front, and a quiet room, I can just barely hear the fans running. If the CPU starts warming up, SpeedFan adjusts accordingly. At full out the fans run at 2200RPM (CPU) and 1200RPM (three case fans). That can be loud, but it generally only happens when we watch a Bluray movie, and that usually has enough noise to cover the fan sounds up.