# Desktop computer case fan slowing way down at intervals - cause? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 28, 2016, 2:31am UTC](https://boards.straightdope.com/t/desktop-computer-case-fan-slowing-way-down-at-intervals-cause/747357 "2016-02-28T02:31:51Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Rigamarole](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@Rigamarole](https://boards.straightdope.com/u/Rigamarole)\ **Post date:** [February 28, 2016, 2:31am UTC](https://boards.straightdope.com/t/desktop-computer-case-fan-slowing-way-down-at-intervals-cause/747357/1 "2016-02-28T02:31:51Z")
I have a Cooler Master case with several fans on a custom-built PC I’ve been using for years. Recently one of the fans on the top of the case started making a loudish noise every 5-6 seconds. I got a flashlight and watched it while running and realized the fan is spinning way down and then spinning back up again to a faster speed, and that is what is making the noise. Strangely, I moved the fan’s connection from one labeled “CHA\_FAN” to “PWR\_FAN” (the only free slot), and it behaved slightly differently. It is running on a lower/slower speed mostly (and not making the noise), but occasionally, it still spins up to a faster speed and makes the same noise when it slows back down. I could replace the fan of course, and I’m hoping that’s all I have to do, but I want to make sure it’s not something else, like an issue with the mobo’s connections (mobo is an ASUS Sabertooth X58). I also remember in the past trying some (possibly 3rd-party) software that was supposed to monitor/regulate fan speed but I don’t think it worked as intended. I’m probably going to try a few more experiments with hooking different fans to different mobo slots (and looking at BIOS settings - there are some for fans right?) in order to further isolate the issue but I wanted to see if anyone had experience with this kind of thing / ideas about what the issue most likely is. Thanks in advance for any advice. ---
**Author:** ![JerrySTL](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@JerrySTL](https://boards.straightdope.com/u/JerrySTL)\ **Post date:** [February 28, 2016, 3:04pm UTC](https://boards.straightdope.com/t/desktop-computer-case-fan-slowing-way-down-at-intervals-cause/747357/2 "2016-02-28T15:04:41Z")
A lot of PCs control the fan speeds based on temp sensors inside the case or on the motherboard. Maybe the inside temp is getting a little hot at times or the sensor isn’t working correctly. I doubt that it’s the fan itself. Have you opened up the case and blown out all the dust bunnies lately? ---
**Author:** ![Rigamarole](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@Rigamarole](https://boards.straightdope.com/u/Rigamarole)\ **Post date:** [February 28, 2016, 10:40pm UTC](https://boards.straightdope.com/t/desktop-computer-case-fan-slowing-way-down-at-intervals-cause/747357/3 "2016-02-28T22:40:57Z")
> [@JerrySTL](#): > > A lot of PCs control the fan speeds based on temp sensors inside the case or on the motherboard. Maybe the inside temp is getting a little hot at times or the sensor isn’t working correctly. I doubt that it’s the fan itself. Have you opened up the case and blown out all the dust bunnies lately? Yeah, I just did that when I changed the fan connection (what’s the difference between CHA\_FAN and PWR\_FAN anyway?), so that might be why it’s staying on a lower speed more now instead. The frequently oscillating speed still seemed a bit strange to me. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 28, 2016, 10:56pm UTC](https://boards.straightdope.com/t/desktop-computer-case-fan-slowing-way-down-at-intervals-cause/747357/4 "2016-02-28T22:56:01Z")
> [@Rigamarole](#): > > Yeah, I just did that when I changed the fan connection (what’s the difference between CHA\_FAN and PWR\_FAN anyway?), so that might be why it’s staying on a lower speed more now instead. The frequently oscillating speed still seemed a bit strange to me. “CHA\_FAN” is probably for the rear case fan. “PWR\_FAN” is usually there for power supplies which have a cable run out so the motherboard can monitor its fan speed. I think in most cases the power supply still powers the fan itself though.