I think it must be either some unknown third-party gizmo mounted under there somewhere or...
The fuel pump. I really don't know how a fuel pump could make that noise so loud, immersed in gasoline, inside a plastic fuel tank. But, that pitch is what I would expect if I ran a fuel pump dry on a bench. It would be great to figure out a way to rule in/out the pump without actually replacing it. Maybe it's a bad bearing in the pump motor and it needs to run a little bit to get up to that pitch of noise.
Ok, let's run through this and make sure we are on the same page:
1) You turn the key to ON, and you hear the fuel pump run for about one second. It's a brief lower-pitched noise.
2) With the key ON with the engine not running, you do not hear the higher-pitched noise, even if you leave it like that for a minute.
3) You start the engine, and you begin getting the high pitched noise immediately.
If all of these are true, then maybe we can make the noise happen by running the pump continuously with the engine off, and if we can, then we can relate the noise to the fuel pump.
If that sounds reasonable, you could do the following:
1) Locate the OBD I connector, it is loose behind the power distribution box (fuses and relays) under the hood. Or it may be clipped to the back of the box itself. It looks like this:
View attachment 316337
2) One of those connectors manually triggers the fuel pump. Here is a diagram:
View attachment 316338
3) Connect the connection labelled 'Fuel Pump' to ground. Ground please, not +12V... +12V would do bad things, it needs to be grounded.
4) In this condition, turning the key to 'ON' without actually starting the engine will cause the pump to run continuously. Turn the key to 'ON' without starting the engine and leave it like that for a minute. Do you get the noise? Can you control the noise by turning the key OFF and ON? If you remove the ground from the connector and do the same thing, does the noise not happen? That would be diagnostic proof that the noise is coming from the fuel pump.
Do not leave the pump running with the engine off for too long, just a minute or so. If you have a leaky fuel injector, it could start filling a cylinder with raw fuel. If you want to do this repeatedly, start the engine for a moment, stop it and try the test again. It's unlikely you actually have a leaky injector, but I just want to cover all the bases.
If this does not create the high pitched noise, I don't think it rules out the fuel pump definitely, it's just a test that might prove it IS the pump.
Anyway, I appreciate that you just graduated, congratulations by the way, and your time may be tight right now. Whenever you get to it, if you want to give it a shot.
Good Luck!