Tercel fixes: Serpentine belts --> small tweeting sound
If your car makes this noise, you will need to replace your serpentine belt.
There are two belts in my Tercel, they are used to convert the energy from the motor to electric devices like the AC and the alternator.
The sound is a tweeting noise, mostly audible when the motor is on, you are not pressing the gas pedal. Spraying some lubricant will temporarily get rid of the sound, but in a few minutes, the sound is back.
Reading online points to the tension of the belt but the car repair shop says it is most likely the belt glazing with time. I got both changed because the effort is mostly to remove all the parts to access the belts.