Mazda Protege squealing noise when idling and driving

I have a 2002 Mazda Protege ES automatic, (2.1 engine) with appx 75K miles. When started the car makes a squealing noise while idling, then while driving it will do the same intermidetly. This noise comes & goes at different times. The only constant seems to be the RPM's are low when it starts making noise, then high when it ceases. Also it seems to be worse when the outside temp is below 30 degrees. After hearing the noise I have had the belts replaced, a new battery & alternator installed along with new front brakes. None of this helped, it only seems to be getting worse. Any idea what could be the cause of this?