How to fix a noisy bottom screen?

Whenever I turn on my DS, the bottom screen makes a loud screaming noise.

For example, monitors and computers all make noises, regardless of the fan in question (No, I do not mean the fan, I mean the screens.)

I've narrowed it down to the bottom screen by covering the top screen, and listening to the (Static?) noise from the front, sides, top and bottom.

It is only when I turn on the DS, and only the bottom screen.

The touch-screen is still accurate and usable.

The pitch/volume of the 'Screaming screen' is not exact, it changes sometimes.

I think the compression of the inner parts may be a factor.

I have not seen the insides of the DS, as I've not had the time, money, or tools required to get a look at what the problem might be, considering that I am a High school student.

This DS I've had for a while, so I may as well state any facts about it, just in case.

The DS is a hand-me-down from my mom, as I started to use it more than her, and she stopped using it altogether. One of our cats puked on it, and some water and elbow grease later, it was cleaned. (Didn't turn on though. May be cause.)

A few months and a small amount of charging later, and it worked again, mysteriously.