USB adapter makes high pitched sound?

---

I just used the usb adapter for the first time today and when I plug the usb cable into the phone the adapter makes this high-pitch frequency sound. It's similar to the mosquito ringtone that teens love so much. It stops when the phone is done charging. Does anybody else have this problem?

I noticed this yesterday, but it was only when the Incredible was fully charged.

I'm cycling the battery right now, so when I plug it in again...I'll get back to this thread.