A little info about your vehicle will help.
(EDIT: Duh, I didn't even look at your screen name)
Assuming it's a 4th gen (since you posted in the 4th gen forum - DUH), I believe there are two ECUs that are mounted underneath the glove box. There's the 4WD Control ECU, and I believe the Height Control ECU or something else is also possibly mounted there as well. I don't have height control, so the only one I have there is the 4WD ECU. A high pitched noise isn't normal per se, however, if you aren't experiencing any problems, it's probably not worth the $$$ to replace unless you are still under warranty.
First thing I would do is determine what the noise is definitely coming from, then operate that system to see if it goes away at any time. I would also take the cover off to see if there is any obvious problems on the board, such as poor solder connections, heat/burn marks on the board, etc.
If you are no longer under warranty, something you may want to try is to wrap it in sound deadener, or some kind of trunk carpet/insulation. Before covering it, you may want to check it to see how hot it gets while driving. If it gets hot under normal conditions (I've never checked mine), you won't want to do that as it will cause it to retain the heat and possibly overheat.
Just a thought.
