A friend got a "new" (several years old) pc from an other friend. The pc made strange noises, so I open it and found a little speaker connected to the USB pins on the mainboard. Not an USB speaker but a simple mini speaker with two cables (see the picture). Why would someone do this?

If it fits...

Just put it in.

The real question:

Why is the person who installed that working on a computer?

Its a piezo speaker so its not really drawing any current/power. It looks like it is on the 5VDC rail. So it literally is responding to current changes on the rail. Kind of neat electrically. Maybe the person who installed it knew some electronics and wanted to troll the end user.

In general assembling a PC is like Lego, until you get to things like this and don't read what the pins are.

Most likely it was plugged in because it fitted, not because it was intended to go there.

@unsignedint illegal lego building techniques

Are you shure this is a USB header ??
This looks to me like the front panel header and if you look in the manual you might find a pc speaker output connected to those pins the piezo is sitting on. And many modern cases simply ship a piezo speaker instead of a real one. So this for me at least looks correctly assembled.

@mee4895 Yup, looks like the front panel headers. So it's just a debug speaker

This is definitely a 9 pin usb connector (for usb ports on the front panel). The sounds of the speaker are consistent with the assumption that this speaker was just connected to the power pins of USB. I'm wondering who mighty do this and get annoyed many years of strange noises.

These speakers can be used for debugging the PC (Hardware not software problems). The Mainboard can play different beep sounds depending on the issue.

If the computer runs fine, you can safely remove it.

Yes, I removed it. But because it was so annoying. It beeped every few seconds (irregularly).

@pythonPlusPlus
Aaaand... We have a winner! Congrats! A single beep at start for you.
@Sumafu
Beeps randomly? Well... That's not good usually.

@JKamue and i am sure that it is a usb connector. In this white piece of plastic are several independent connectors.

instructions unclear, dick stuck in pc case

@IntrusionCM and if it doesn't work

just try it again

@IntrusionCM If you are using this rule during sex, you are going to have a really bad time.

Damn I haven’t seen one of those in a long ass time lmao