I HAVE A 1999 CHEVY CAVALIER LS 2.2L AUTOMATIC, ABOUT 59000 MILES ON IT BASICLY IT JUST RECENTLY STARTED MAKEING THIS WHIRRING/ WHINNING NOISE, IT SEEMS TO MATCH THE IDLE SPEED, IF YOU PRESS ON ACCEL. IT GETS FASTER AND LOUDER, ETC, I MAY HAVE NOTICED A POWER DECREASE ALSO, BUT NOT SURE IF THAT IS RELATED, ALSO AS YOU DRIVE DOWN THE ROAD THE LOW COOLANT LIGHT WILL FLICKER ON OCCASION, I HAVE CHECKED COOLANT AND IT SEEMS FINE, DO YOU HAVE ANY CLUES?
Without hearing the noise, it is really hard to tell.
If it matches the engine, then maybe it is your altenator bearing starting to make some noise. Have you tried to open your hood and see if you can tell if it is the altenator making the noise?