2001 Toyota ECHO

I recently bought a 2001 ECHO and am delighted with the car. However, there is one interesting characteristic of the car that I am curious about. It seems like, as soon as the car is warmed up, I hear a high-pitched sound (very much like the sound of break squeal) when the throttle is in a certain position (or maybe is it a certain rpm). If I alter the position of the accellerator the sound stops and I only hear it when the accellerator is in that particular position. However, altering the position of the accellerator of course results in going faster or slower than desired, so I hear this high-pitched squealy sound quite a bit. Thanks for any knowledge about this that might be out there.......

hey ronald.... this is sooo weird because mine does that too and there's this other girl at my school that i like kind of know who got the same kind of car except hers is blue and mine is red and so does hers. its like you hear it when the gas pedal is in a certain position and it sounds like a really totally high pitched sound like kind of a squeal or like hissing kind of sound. it comes from under the hood of the car but i dont have a clue. i got mine for an early graduation present and its a really cool car but i dont know what that sound is either.......

Could it be a whistling sound from the throttle body??? I know that on certain vehicles an aftermarket TB spacer can cause this sound, but this is first time I've heard of anything like this on a stock vehicle.