Engine whine when accelerator is pressed (2000)

Hey everyone. Hopefully someone can shed some light on this.

Let me state up front that I am by no means a car expert of any sort. That said, I'm an engineer by trade so I think on a technical level and learn quickly.

Background: I bought my 2000 Mitsubishi Mirage a couple years ago with 55k miles on it. I've maintained it reasonably well, changing the oil every 5k and having a little work done here and there (I can be more precise if need be).

Issue: Recently, around 77k~80k (it's now 80.7k), my car developed a high-pitched whine. It only sounds when I press the accelerator past a certain threshold (~20%, maybe), and doesn't seem to happen consistently in the lower gears. It is, however, constant and consistent once I'm maintaining speed at 45mph or higher. I believe that it's coming from under the hood, but I'm not 100% on that.

Suggestions: Upon hearing it, one friend suggested that the problem may be with my fuel pump. Another mechanic suggested without hearing it that it might be my timing belt since I didn't get that replaced at 60k. I don't know how to confirm or deny either of those suggestions other than to get a second opinion.

Any help is appreciated! Thanks.