whining noise under the hood of 2001 Jeep Cherokee Sport

I have a 2001 Jeep Cherokee Sport with just over 50,000 miles that just started to have a high pitched whining noise coming from under the hood once I get up to about 30 mph. The noise persists even when gas pedal is not pushed as well as when it is shifted to neutral and is coasting, as long as it's above 30 mph. It is a 4.0 L 6 cylinder engine that has had good care. I just moved and don't know any reliable mechanics in my area. Any info. would be greatly appreciated.

T