Noise from fan

[John]

If I shut down using Windows the number lock light stays on. If I unplug
from the mains or use the power switch on the back of the PC I find that the
fan makes a noise for a couple of minutes when I start up again. It sounds
like dry bearings.
I can't understand why it only makes a noise if I have completely powered
down. What drain may it have if I do not power it right off?

The board is a ASUS A7S8X-MX

 

[Jan Alter]

It's possible that the fan axle or bearing does not completely settle into
its cage while there's a small bit of power still supplied to the fan. Once
the charge is removed the axle bottoms out, and because the bearing really
is dry it takes a few moments for it to spin up from the bottom so you don't
hear the noise anymore.

 

[Paul]

If I shut down using Windows the number lock light stays on. If I unplug
from the mains or use the power switch on the back of the PC I find that the
fan makes a noise for a couple of minutes when I start up again. It sounds
like dry bearings.
I can't understand why it only makes a noise if I have completely powered
down. What drain may it have if I do not power it right off?

The board is a ASUS A7S8X-MX

When you select "shutdown" in Windows, the +5VSB is still on.
The power supply still converts some power, and is drawing at
least 10W from the wall. There is no air movement through the
PSU while in soft-off, which means any heat generated by the
+5VSB circuit, stays inside the supply.

That means there is a difference in the internal temperature
of the PSU, between "soft-off" and unplugging/switch-off-at-back.
If the room is reasonably cool, the unplugged computer's fan
starts off at a fairly cool temperature.

Paul

 

[kony]

If I shut down using Windows the number lock light stays on. If I unplug
from the mains or use the power switch on the back of the PC I find that the
fan makes a noise for a couple of minutes when I start up again. It sounds
like dry bearings.
I can't understand why it only makes a noise if I have completely powered
down. What drain may it have if I do not power it right off?

The board is a ASUS A7S8X-MX

Depends on what power management state the system is in when
the numlock is on. If it is completely powering down the
system to S5 state, it should equally cause the fan to make
same sound when starting again, unless the system hadn't
been turned off for as long so it was at a different temp,
or because having it supply 5VSB to the system will slightly
raise the temp inside the power supply so the fan may have a
different amount of play in the bearing.

It's beside the point though, there's no need to know why,
only that you need a new fan or to lube the present one (if
a sleeve bearing fan). Keep in mind that when an fan
finally fails, often it is seized and doesn't spin at all
upon powerup, which is easy to not notice since it is then
silent.