I have a loud engine noise--somewhat high pitch whine--except really loud and only after so many rpms. The noise happens when I am running my air conditioner. Ten to 15 miles after I first noticed the sound, my serpentine belt came off. I had the belt and tensioner replaced, but the noise is still there when I turn on the air conditioner.

Seven ways to pinpoint that high-pitched, whining noise

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Oct 2, 2013 - I recently had new fan belts installed after hearing a high-pitched, ... Do you hear the noise when the engine is running and the vehicle ... Just replaced water pump (and timing belt) yesterday and squeal ... When driving it make a noise but change out and caught speed the noise is coming from driver side.Missing: 1999 ‎plymouth ‎breeze

What is causing that irritating noise? ' DSMtuners

Troubleshooting Strange Sounds Coming from Your ...

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You hear a high-pitched squeal that stops when you shut off your engine: Readjust or replace the belt. These belts should have about half an inch of play and ...Missing: 1999 ‎plymouth ‎breeze

Possible bearing in one of the drive pulleys. I have changed numerous alternators for this noise. Take the belt off and start the car. If the noise goes away you know it will be pulley related and not transmission related. If noise goes away, spin all pulleys by hand to determine the defective/noisy one

remove the belt and start the engine ..IF THE NOISE disappear it might be idler bearings that driven by belt but if the noise still there check the pcv valve..

The pump is designed to run when engine is cold to clean up the exhaust, they do make a high pitched noise and this is not abnormal in any way. They are very much like a high speed blower dryer in the way they move air. You can't replace parts in them, they are sold as one unit cost about $210.00 US. A new pump will be somewhat quieter but is it worth the cost and time to replace it? Here is a picture of the
pump. Just click HERE

Does the high-pitch whine exist when the engine is just running? Not moving (transmission is not in gear)? Running but with transmission in neutral (coasting down hill)?

Your noise is called over-run and its in the gearbox which is also the diff and thats the noise you are getting .
Its the meshing up of the crown wheel and pinion and the only way out of it is to replace the GEAR BOX ASSY with a S/Hand one as you dont get to many doing that noise.
Let me know how you get on. RON

you could be low on transmission fluid check that and make sure it registering properly on the dipstick.

Sounds like a dry/failing bearing or power steering pump noise. You first need to try to track down where the noise is originating, and the most likely place is at the front of the engine.
I would start by listening with the hood up while parked with the engine running and the noise present, and seeing if it is coming from there. If so, the most likely cause is something connected to the belt - e.g. AC compressor clutch, tensioner, power steering pump, or generator. Can also be caused by the belt just slipping (warn out belt, tensioner not working properly).

This Noise Description sounds Indicative of the Sounds that come from the Serpentine Belt Or Related parts such as Belt Idler Pulley or Belt Tentioner witch also has a Pulley, but if Tensioner itself is Literally BROKE I've replaced a number like this it will cause a Whining noise . Best case scenario its just the Belt, and if any of the other Problems turn out to be the Culprit the Belt MUST be Replaced Anyhow as Damage is Being caused By the Very Whining you hear.
PLEASE Spend the Extras $ for the BEST BELT as this Drives your Water pump, Alternator, A/C Compressor, Power Steering Pump All Crucial to Control of, easy Steering ,All Electrical-Power Distribution, The COOLING of Engine << VERY CRITICAL Component
The Pulleys usually have a more Hum type Whining. So I would say at Best The BELT , And WORST Belt Tentioner is Broke

Have you crawled under the vehicle and personally inspected your exhaust line from manifold to tail pipe? The roaring sound usually occur when there is a hole in the exhaust line. I had it happen to my forester before. A hole half the size of a dime made my subaru sound like my old 74 chevy pickup.