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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?

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A fan speeding up is intended to counteract your system heating up. So, either your system is actually heating up (maybe you are playing a graphics intensive game or something) or your system "thinks" it is heating up when you are in single monitor mode.

With respect to the fans immediately quieting down when you switch from 1 monitor mode to 3 monitor mode: it doesn't make sense to me that they are correlated unless the configuration change changes the fan policy in your system in some way.

Otherwise, I know of no reason for you fan speed to be affected by your monitor configuration.

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Guess it might be a setting somewhere. Any idea where I'd look for that? – Ian Varley Oct 25 '09 at 19:38
Fan control can vary depending upon the motherboard design. My understanding (as a motherboard hardware designer) is that it usually resides in the BIOS tells the OS using an ACPI interface. One way to override is covered in the question superuser.com/questions/29049/… Fan control can also run autonomously via SMBus, Super I/O or Application Specific IC devices based on temperature reading(s). – hanleyp Oct 26 '09 at 0:02
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