Weird noise from speakers when powering off PC

Huge storm in my area tonight, and lightning is striking near my house, so I shut off the PC and disconnected all the wires so nothing can happen to it.

When it was shutting off, when it was on that windows screen that says "shutting off" the speakers began making a high pitched squealing sound while it was shutting off and the noise stopped after the power was gone.

I'm curious as to what the source of this noise actually is.

Was your speaker cable plugged in all the way into the jack?

Is it still doing it? If not it could have just been some static.

Yeah it's plugged in all the way. For some reason it squeals when powering off though