I've recently built a PC (), which essentially consists of the following:
Motherboard: ASRock H77 Pro4/MVP
CPU: Intel Core i5 3450 (using the stock heatsink & fan)
RAM: Corsair 2x4GB DDR3-1600 XMS3
GPU: EVGA GeForce GTX 560 Ti
SSD: Samsung SSD 830 Series 128GB
PSU: be quiet! Pure Power L7 430W
Now, the system is running perfectly fine so far and I haven't had any issues yet, but there's one thing that somewhat annoys me. When booting the system, the CPU fan seems to start about 3 seconds after everything else has already started (case fans etc.). Essentially, after pressing the power button, I can see the fan "twitching" twice (it starts moving a little two times), then it spins very loudly (presumably at full speed?), but slows down immediately to the speed it normally spins at. As I said, it takes a few seconds until it actually starts spinning at full speed, as opposed to the case fans, which start spinning immediately. All fans are connected to the motherboard.
The fact that the fan starts at full speed and then slows down doesn't really bother me, my old AMD CPU did something similar (unless there's a problem with that). However, the delay is strange to me. If I look at the CPU temperature in the BIOS immediately after starting, this doesn't seem to overheat the CPU; in fact, it runs rather nice and cool (about 35°C), but because I've put together the thing myself, I want to be sure that I didn't mess anything up. Basically, what I'm asking is whether I need to worry or if this is normal.
Thats normal, some mobo/CPU heatsinks work together like that. One of my old PCs does that and my sister is still using it 7 years later. My current PC did that with the stock heatsink but not with my current one I use for OCing.
Don't forget that the cpu heatsink fan is pluged into the cpu fan header on the motherboard and that is controlled by the bios. That means that the fan will come on when the bios tells it to and when you first turn on the Pc the cpu is not hot so there's no reason for the fan to spin. Once the cpu heats up then the fan comes on to help cool it down.So this is pretty much normal and will not be something to worry about. Also different bios versions will act just a bit different from one another since they have different instructions so your friends computer might start up a bit different from yours.
Don't forget that the cpu heatsink fan is pluged into the cpu fan header on the motherboard and that is controlled by the bios. That means that the fan will come on when the bios tells it to and when you first turn on the Pc the cpu is not hot so there's no reason for the fan to spin. Once the cpu heats up then the fan comes on to help cool it down.
Well, I don't really think that it's because the CPU isn't hot at the beginning, because just moments later the fan starts at a completely over-the-top, excessively loud speed (even though the temperatures show that the CPU is fine), just to become quiet immediately afterwards. It's just so weird that I doubt it's "intentional" behavior.
But anyway, if it's just a motherboard- or fan-specific quirk, I can just ignore it.
It may even be a feature designed to blow the dust off , I've heard of some fan/heatsink connected to a bios controlled fan header actually starting up full force in reverse to do just that and then stop and run normally.