'94 high pitch squeal

94 eldorado. When my engine is running my car will make a loud high pitch squeal, not quite as loud as poor break pads but about the same pitch and as annoying. It makes this noise regardless of whether I'm moving or stopped. But, when I press on the gas the noise gets lower and quieter relative to how hard I'm pressing the petal and will go back to how it was when I let go of the petal. Anyone have any idea what this could be?
Thanks,
Blue21

Vacuum leak one possibiity, without hearing it tough to tell, if not, remove the belt see see what happens.