Who's stealin' the juice?

[UncaDanno]

One of you builder types may have experienced something like this. One of my boxes at home is cheap-o deal I got in order to step up to a PIII.
The mobo is a PCChips.

(Pause to let you stop laughing.)

It's a Slot-1 w/ a PIII 450Mhz. The rest is pretty immaterial except for the cooling fans and the PS.

Soon after getting the system (it was like paying for the CPU + $10 for the rest of the setup) I got a "real" case with a 250W PS and more drive bays. Also got an additional case fan (direct power from the PS) and a bay cooling fan (ditto). The CPU has temp-controlled fans and the PS fan is always-on.

Here's the deal. After the machine has been running a couple of hours, the high-pitched sound of one of the fans starts to fluctuate depending on the load on the machine.
For instance, if I do something to change the state of the display, say scroll down a list, the pitch of the fan lowers a bit until the screen paint finishes. Likewise, if something happens to cause disk I/O, the pitch lowers with each disk access.

Just started doing this the past week. I've had the system for 5 months now. And I have neither added nor removed any devices that would change the load on the PS in that time.

Any ideas what may be causing the PS to seem to suffer?

Thanks

[topflite51]

Since this occurs after machine has been on for a couple of hours, suspect problem is heat related. Check operation of fans, ie speed, another fan may be running slow to start with, or slow down after its been on for awhile.

[Axel]

Are you running with less than 64 MB of RAM in your system?

If you have that fan in line with the PS of your primary HD, then you might have the following problem.

Running with less than 64MB RAM on a win 95 system and then loading it up with programs means you might be accessing the swap file on your hard drive a lot.

If your hard drive is about to go out, it might impact the power going to the fan causing it to act as you describe.

So - you might check available resources and whatever is running in your "close programs" screen when next you hear it.

That's the complicated answer, another one might be that you just got a bad fan which eventually over-heats causing a brush to bend in enough to cause it to slow and become noisy.

You might also just have a bad power supply on your hands.

So - first question - take off the case and identify the fan making the noise and which component it is in-line with from the PS.

Next - what's running within your system when it happens?

[UncaDanno]

I've been toying with the idea of yanking the side of the case off after an hour or two to see if I can determine which fan has the variable whine. I'm skeered it's the fan(s) on the CPU since they're temp-controlled and the high-pitched whine starts after the system has been up a few.
I can look at the temps and the CPU fan speed in the BIOS setup. The other fans are just dumb run-all-the-time affairs.

Anybody know of any Windows-based utilities that'll give the same vital signs as the BIOS setup?

[UncaDanno]

I have 128MB of RAM installed.
And the variation in the whine occurs just whenever anything changes in the state of the apps. I can have nothing but Explorer running and a drag of the thumb slider can cause the pitch to change.
But your comment about the physical connection got me to thinking. I think I have the bay cooler piggybacked with the master CDROM. Shouldn't cause the variation, but could be the source of the whine. Cheapo fans.
The additional case fan is connected to a pigtail of its own. But I'll check. It's a big honker. And is not tmep-controlled. If I got it chained in with one of the HDD PS connector, I could be putting too much of a preload on that particular part of the circuitry.

Thanks