I inherited a Lenovo Desktop (3000 Family, 'J' Series), vintage 2006. When I power it on the case fan spins at five to ten times normal speed for about twenty seconds, then slows down to normal. What a blast! Just wondering why this happens. Maybe some undocumented feature?

"When I power it on the case fan spins at five to ten times normal speed for about twenty seconds, then slows down to normal". It may sound like that but I'm confident the fan isn't turning 5 to 10 times normal speed. I would guess you may have some defect in the fan that settles down after a bit. Sleeve bearings can wear out or even spin out in the holder. Probably need to replace that fan. Get one with ball bearings.

As OtheHill said, your case fan is about to fail. When you start the PC, the fan ( and everything else ) is cold. That's why you have too much noise because worn parts inside the fan ( spindle and bearing ) have excessive clearance. When the fan warms up, the excessive clearance tightens up due to thermal expansion of parts and the noise diminishes. If you continue to use that fan, it will fail some time depending on your usage of the PC. Be sure to have a replacement at hand. Check if you can fit a bigger fan. Some cases are designed to accept several sizes of fans. Regards SuatCINI

Many new motherboards and video cards will run their fans at maximum speed during the POST process. My guess is that this is a safety feature. During the startup process, before the system and video BIOSes are able to read the temperature diodes scattered throughout the PC, they'll run the fans at maximum speed. It's a "just in case" kinda thing. :P You should hear my computer when it powers up, the loud little son of a lemon cake. The CPU fan blasts away for a few seconds (until the POST beep), and the video card fans run at top speed until Windows loads the video driver. The creme de la creme of Socket 939: Opty 185 @ 3.2GHz SLI'ed GTS-640s, both flashed to 625/1458/1950 4GB PC3200 Blu-Ray/HD-DVD, X-Fi A8N32-SLI Deluxe 3DMark06: 13896

Thanks, JackBomb. Yours is the only response that makes sense. Perhaps I misled the others by failing to mention that this PC has exhibited this condition from the time I first installed it for its former owner. Now that I understand, it's kinda reassuring. Regards, howagood

To verify that jack's explanation is what is happening look at how the case fan is connected. If connected to a MBoard header then jack's explanation may be correct. If connect to a molex power connector then there is no way any smart sensors can function.

I'm with jackbomb. I have a Fujitsu Siemenns E600 that does the same thing. Before posting try google. Backup. Use anti virus software.