High pitch sound

[powergrip]

I was driving the other day and I heard an odd sound coming from the stereo deck area. It was distinct but too quite/high pitch to pinpoint the exact source. I know it wasn’t me because my brother in the passenger seat heard it too. The radio was on and we heard it clearly, so I changed the channel to see if it was the radio. It continued. So I turned the radio off completely. It was still there. I got really annoyed so I tried to drown it out with music. It eventually went away. I don’t know when or why but it did.

Any else experience this?