High pitch sound while charging...

[xMimixVera]

I have a LG Optimus Slider from Virgin Mobile. When I first got it, I charged it and everything and I noticed this high pitch sound. My phone charger is a usb. You can charge it on the wall or plug it in into your computer. It's really frustrating because all I hear is that high pitch sound and it sometimes don't even let me sleep when I'm charging it at night. Gives a slight headache..
Please let me know if you know how to fix this problem!!
Thanks!