I have a Core i7-930 being cooled by air with a Prolimatech Megahalems, RevB and two 120mm fans in push/pull configuration. The push fan is a three-wire fan connected to the CPU fan header on the motherboard. The pull fan is a four-wire pwm fan connected to an Opt fan header near the mb i/o plate. The odd behavior I'm seeing involves the pull fan. There are times when this fan is not running at all even though I don't believe there is any speed modulation connected with the Opt header--it should be running all the time. The push fan does run all the time. If I rap the pull fan housing lightly with a small metal tool or flashlight, the fan starts spinning and will remain that way until the machine is put to sleep or shutdown. What in the world could be causing this fan to require a light rap to get it going?? Anybody have any ideas on this? Thanks. John Hixson