Windows notification sounds while computer is idle and locked

I have a Windows 11 Personal machine that is driving me nuts.

When the computer is idle and locked, I randomly hear notification sounds, similar to a USB device being plugged in.

I've tried disabling all notifications and it still keeps happening.

This computer is left powered on all the time, and I randomly keep hearing these notifications from other rooms in the house.

Any suggestions appreciated!

Welcome to the forum. More often than not, the chime sound plays when a peripheral device is connected or disconnected from your computer. A malfunctioning or incompatible keyboard or mouse, for example, or any device that turns itself on and off, can cause your computer to play the chime sound. USB hubs and drives are often the culprit as well as usb printers. Other causes of chiming can be incoming emails or loss of scan to computer function.
Disconnect everything to see if the problem goes away. Then connect devices one at a time until you find the right one.

If the sound persists after all peripheral devices are disconnected, you can turn the sound off but this will not tell you exactly what is causing it. It will, however, give you more indication of what is making it happen. Right click sound icon in task tray>sound settings>more sound settings>sounds tab>
click the "Test" button next to each Program Event until you locate what event is causing the sound you are hearing.

If you choose, you can disable the offending sound by clicking the "Sound" pull-down menu and selecting "(None)." but it's best to find the cause rather than covering it up.

I m not an computer expert but i think i had similar problem with HP Z 400 desktop with windows 7 hooked up to two monitors.
It happened when I replaced an old dead LG monitor with a new Samsung monitor early 2025.
New feature of the new monitors may be checking their input signals? - Because the new monitors can be connected to one or more different devices?
I had a hint that the noise may be coming from devices notification sound being connected / disconnected etc (mouse/keyboard/usb devices etc. What about a monitor? - I asked myself)
Finally i unplugged the new monitor after the keyboard/mouse etc.
The annoying sound during the 'Sleep Mode' stopped for me.
Then , knowing the problem comes from the new monitor I looked up the function switches / modes etc.
I cannot remember what I did but I changed something on the Monitor function - (probably asking not to check the inputs automatically because i am using the monitor from only one Input source - my desktop computer - I told the monitor I will choose the input source manually, i think
That is my happy experience without the ding /dong noises - now for a few weeks.

I wonder if an internal device or its connecting cable might be loose?

If you have external speakers, turn them off? Sorry, couldn't resist. I noticed that issue as well, a little aggravating but we have several computers as well as tablets, phones etc. that all announce notifications. I tend to ignore them all.

Look in the event log and see what is being "connected" or "disconnected".