I have a 2004 Jeep Grand Cherokee 6 cyl with 91000 miles which recently developed a high pitched whining sound coming from the back of the car . It exists when idling along with accelerating.

SOURCE: High Pitch whine during acceleration

First you need to isolate the noise. You don't mention the mileage on the car. Do you have the supercharged engine? If you do, remove the belt for the super and make sure that is not the problem. If you still hear the noise approximately below or from the super area, it is most likely the belt tensioner pulley.
In my car there was a large washer over the pulley (original equipment), as the pulley wobbled on the bad bearings, it would cause a sound like a bad alternator or gear whine getting exponentially worse the faster the engine reved. Now that the part is replaced, you can barely hear the engine idle and is significantly quieter at high RPM.
My car - 2004 Pontiac Grand Prix GTP with 66,000miles.

SOURCE: A high pitched whining noise in the engine.

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

SOURCE: High Pitch whine during acceleration

Hi Pullerwife,

I have a few suggestions for you,

First of all, check your air filter, make sure its clean, not clogged, and doesn't need to be changed.

I don't know how handy you are, but if you are fairly handy, check the idler pulley bearings, if your not, have a shop check it out, as a last resort.

Power steering pump/fluid being low is also a possibility, but thats usually more of a lower pitched whine then what you describe.

You say once the vehicle is warmed up, the whining stops. Does Weather seem to be a factor as well?

Hope I've helped, and don't forget to rate.

Lazaruselite

SOURCE: Whining Noise

Hi, this sound is most likely coming from the power steering pump. I would first, check the power steering fluid level to see if it is full. if its not at the full mark, add some fluid. If the fluid reservoir is full upon inspection and the whining continues, the pump may be damaged and the pulley on the power steering pump could be slightly out of sync with the pump housing.

The second issue could be belt slippage. i would do a tension check on the drive belt and pulleys as well. make sure there isn't any ware and tare on the belt and make sure the tension is to specs.

Please rate and god bless:)

SOURCE: MPV 2001 burning smell, high whine?

Sounds like either a fan belt or a drive belt needs to be replaced...