When booting windows xp in safe mode the noise starts right after the last line which is MUP.SYS, so the noise starts while it is still showing text mode on screen.
I also tested the pc with more modern PSU and it didn't make any difference.
Can nobody help me with this problem?

I tried installing win98se. There is the same noise. Except that in networking login screen everything is still quiet. It is also quiet during any driver installations that happen after boot before the desktop shows up. It is only after I click "ok" and it loads something from hard drive for a second the noise starts. Another thing is that some things I do make the noise disappear for a bit. For example if I open dos prompt, it is quiet when I am typing text in dos prompt and continues after I am not pressing any keys anymore. It is also quiet while left mouse button is pressed if I click the top bar of any window to move the window to different location.
Also restarting in ms-dos mode makes everything quiet while in ms-dos mode.
Strange problem, isn't it? 😜

Can you post your system specs, including motherboard and anything that you haven't changed in the PC? Also, I would remove the board from the case and try running it outside the case. This will eliminate a chassis short or grounding issue.

Try the easiest thing first, just in case: connect the pc directly to a different outlet

It is the super socket 7 system I have been playing with recently.
Motherboard is SY-5EHM pre-1.0 rev Made in 1998. Manual is here https://www.manualslib.com/manual/715360/Soyo … r-7.html#manual
it came with 01/05/1999-VP3-586B-8669-2A5LES2AC-00 EH-1BC1 5eh-1bc1.bin bios
I took a risk and updated it to 5eh-1da1.bin bios even though it is meant for rev 1.0 and my motherboard is pre 1.0 without any rev number.
The pc came with K6-2 300Mhz cpu which I changed to K6-3+ 400Mhz cpu
Originally for several days I only used dos there, so I didn't know anything about this kind of problem.
I changed the original 512Mb hard drive to 120Gb WD1200 hard drive and installed and toshiba sd-r5112 optical drive so that I could try running windows xp in it and that is when I first noticed the noise.
Things I have not changed in the pc after I discovered the noise are the motherboard, floppy drive optical drive and the hard drive. Power cable and the vga cable have also been the same during tests. Everything else has been changed.
I just tried changing to non-grounded outlet and it didn't change the noise.

Try with the board outside the case. Also, you could try disabling any power related settings in the bios. It could be anything...

Weirdest thing happened. I was messing around with things in windows 98 with drivers and everything. I managed to mess things up badly enough that in windows pretty much all the devices disappeared from device manager and instead there was plug and play bios failsafe device there. I pretty much had to install first optical drive drivers that I could access the win98 install disk and then I had to install plug and play bios again that it would start installing every single device again when I rebooted. It took forever to get things bad to normal.

Funny thing though. The noise is gone. It disappeared when all the devices disappeared from the device manager and didn't come back even after I had installed everything back to normal.
This makes me so confused about what was causing the noise. It must be software or some driver in windows or something like that. I bet it would come back if I re-installed windows, so I don't consider this to be solved just yet.

Edit: Another thing that is different after that mess is that I used to get stuck at "windows is shutting down" screen, but now I get "it is safe to turn off your computer" screen.

It really sounds like you have an electrical problem. When I first read your issues, I thought perhaps you had some sort of grounding issue. It is the same reason why it was suggested to remove your board from the case as well as try another outlet.

The fact that you have experienced the same problem with multiple operating systems, changing cards around hasn't made a difference.

I'm starting to lean toward the obligatory, "it is the capacitors..." statement. I believe you have some electrical instability that is wreaking havoc, and your hardware is fighting the problem and mostly losing. Bold statements, but you have some really odd things going on that stretch beyond simple IRQ conflicts.

Regarding your shortage of AT power supplies - doesn't that board have dual power inputs for both AT and ATX?

yeah, it has both power connectors. That is why I was able to test newer atx psu earlier to make sure there was nothing wrong with the AT PSU that came with the PC. I also measured the voltages while under load with the AT PSU and they were pretty good 12.15V and 5.07V, so it felt like a pretty good AT psu to me.

I knew from start that it always could be bad capacitor or something else wrong with the motherboard, but I wanted to try everything else possible. I am not very good with the soldering iron. I tried practicing desoldering capacitors on broken celeron motherboard with soldering iron and some solder wick and I only managed to get one out and just made a mess of the second one I tried. I need alot more practice before I would try to recap a motherboard I would want to use.

The motherboard isn't all bad because it was stable in winxp 1.6V 400Mhz K6-III+ at 2.2V and 6x100Mhz when I tested it, but that was just testing because there is probably no point in overclocking old parts permanently.

This might be out in deep left field, but... have you tried swapping the RAM?

Yeah, I have. I used to have 2x64Mb and now I have a single 256mb stick. I also just used another hard drive and installed windows xp pro again, so now I have 2 hard drives and one of them has win98se that became quiet and windows xp that is noisy and I can switch between quiet and noisy just by switching the ide and power cable between the hard drives.

Noise in windows xp is much louder than windows 98se ever was and none of those things like typing in ms-dos prompt or clicking the top bar of a window to move it make it go away.

Edit: not sure why this topic was moved to sound forum because this is definitely not a sound issue. It is more likely a motherboard issue or windows issue.

Eep386 wrote:

This might be out in deep left field, but... have you tried swapping the RAM?

I can't see where you say what sort of sound card you're using or whether the sound is onboard. My P100 system has onboard sound and it can output audio from the sound card through the PC speaker. It can also play sound live coming through the mic/line-in inputs. If you had the mic boost enabled in the mixer and nothing plugged into the mic socket, then it would pick up a strong electrical buzzing that would respond to the PC doing things, like moving the mouse around, and send it out the PC speaker.

The solution for me was to mute the mic and line-in inputs in the mixer.

It is highly unlikely to be a grounding/electrical problem as the traditional (non-sound card linked) PC speaker is controlled via a digital output which by default is off, and it's only on momentarily while it's generating a square wave. So if there was electrical noise on the PC speaker cables, you'd never hear it due to the way the speaker is controlled (unless you wrote your own program to turn the speaker on and leave it on.)

Also, how loud is the noise? Don't forget these systems came from an era before quality audio arrived on home computers, so a bit of faint buzzing is pretty normal. Most people couldn't hear it anyway over the sound of the PSU fan and hard drive.

I did not think sound card mattered because there is no on board audio and the noise is still there even if the only expansion card is the graphics card in the system. AWE64 is the card I have tested the system with mostly.
The noise happens only in windows. If I use dos 6.22, there is no noise whatsoever and pc speaker works normally. When windows xp boots and there is the logo screen "windows xp professional" the speaker starts making low crackling noise. The noise changes to louder whining noise when you move mouse cursor or during heavy hard drive access and that noise is loud enough that I can hear from next room. Not as loud as normal pc speaker beeps though.

And the noise disappears when you unplug the PC speaker from the motherboard... correct?

Sounds like some sort of lack of shielding or interference, but it's weird that it's not present all the time that the PC is turned on.

Yeah, it disappears if I unplug the speaker. It would funny if a speaker was making noise while not connected to anything 😜
Perhaps windows drivers activate some feature on the motherboard that is not in use in dos. These kind of things are really hard to figure out.

So the reason I went the electrical issue path is because I assumed odd things started happening on their own in device manager (for instance - a reboot or whatever and suddenly all your devices are reinstalling themselves), however it sounds like you were just messing with drivers?

Drivers:
As for your device manager redo, it sounds like power management ACPI changed. When running an AT power supply, you'll see that "now safe to shut down..." after Windows is done shutting down because you have to physically toggle/flip the power switch to power down. With an ATX PSU, utilization of +5vsb, and a momentary power switch combined with a mobo that supports it, the computer will automatically shut down.

It sounds like perhaps your OS went to a more AT friendly setting. Not sure if you messed with power management/ACPI in your BIOS at some point.

Sound:

PC speaker is controlled via a digital output which by default is off, and it's only on momentarily while it's generating a square wave. So if there was electrical noise on the PC speaker cables, you'd never hear it due to the way the speaker is controlled (unless you wrote your own program to turn the speaker on and leave it on.)

It might be controlled that way but is still ultimately a cone with a magnet that is happy to push/pull given some noise, right?

I might have loaded the bios defaults at one point when this was happening and I also changed PnP settings in bios when windows 98se lost all it's PnP devices and bios fail safe device showed up
Though even if the win98se installation is quiet, the noise started again during the winxp installation to the different hard drive pretty much immediately when winxp installation went from text mode to graphics mode.

The difference between winxp and win98se was that during win98se installation everything was quiet and noise only started when everything was finished and you had a desktop. I just assumed it was caused by something that winxp loads much earlier and win98se loads when the desktop shows up

crackling sound from speakers can also be the walloutlet has no ground cable

I might have an idea what might be causing the noise. It might be caused by OS using ACPI. In windows 98se installation where the noise is gone, ACPI is also gone from the device manager after that mess with the drivers while the XP installation still have ACPI drivers there even though ACPI is disabled in bios.