This is more of an "idle curiosity" question, but here goes.
I've got a desktop tower (a Dell Precision T3400). It's got 3 monitors. Sometimes, when I disable two of them (leaving only the center one enabled), the fan on the computer goes into high gear and makes a lot of noise. It doesn't happen right away, but I notice it because when I reenable the other two monitors, the second I hit "OK" on the properties window, the fan immediately quiets down.
What the heck?