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Ok, here's a question that has my husband and our mechanic stumped. What would cause my Jeep to make this whining, pulsating noise when I get to over 20 mph.? It sounds as though the whine - woo woo woo - noise is coming from something that turns, such as the driveshaft, a belt, a wheel, something like that. The pulsating whine/squeal noise speeds up as I speed up, and slows down as I slow down.  
 My brake's were just replaced, so it's not that. They  went over all of the belts, and couldn't find any loose brackets, etc. There is no  noise until I get to over 20 mph., as I stated before, so it's not the engine. I suggested that it's something vibrating, such as something loose underneath somewhere, or even the luggage rack, or something is rubbing against something that turns. But the menfolk say ' No, it's not that.' Also, the noise comes and goes, and is sometimes louder than other times. The noise is definitely coming from outside the vehicle and not from the speakers.
 Any suggestions out there?  

Too many things to check on this. Watch the tranny fluid condition on this vehicle, I reccomend that the fluid and filter should be changed every 24,000 miles. Could possibly have a bearing going bad in the alternator or water pump, perhaps the power steering pump.  

I vaguely remember this in my 97 Jeep Grand Cherokee.  The bearings in the power steering pump were the culprit.   Good luck.  

Thanks for the replies! We did have the transmission flushed, etc. last fall. The problem wasn't happening then, but it had quite awhile before that, but had quit for a long time. The problem just started again recently.
 Hmmm.... the water pump, alternator bearings, or power steering pump, good suggestions. Here's another thing that could be just my noise paranoia going on from the whining, but it seems that recently I hear a kind of whooshing noise while I drive. It's hard to explain, but it also sounds like it's turning, like a belt that is sluggish but not squealing. This sound also speeds up when I speed up, and it IS present at idle, just at a lower speed. This seems to be coming from under the hood, right around the steering column area (drivers side). Like I said, this may be nothing, it's just that the noise problem has be all hyped up, so I may be just noticing every little thing.
 I know that the water pump is under the hood, as well as the alternator. Where is the Power steering pump? If the whining - woo woo woo - noise were present at idle, it sure would be easier to diagnose. So unless I have someone run along side of me at 20 mph. or more, it's hard to pinpoint!  

check the wheel bearings  

Sue wrote:

Ok, here's a question that has my husband and our mechanic stumped. What would cause my Jeep to make this whining, pulsating noise when I get to over 20 mph.? It sounds as though the whine - woo woo woo - noise is coming from something that turns, such as the driveshaft, a belt, a wheel, something like that. The pulsating whine/squeal noise speeds up as I speed up, and slows down as I slow down.
My brake's were just replaced, so it's not that. They went over all of the belts, and couldn't find any loose brackets, etc. There is no noise until I get to over 20 mph., as I stated before, so it's not the engine. I suggested that it's something vibrating, such as something loose underneath somewhere, or even the luggage rack, or something is rubbing against something that turns. But the menfolk say ' No, it's not that.' Also, the noise comes and goes, and is sometimes louder than other times. The noise is definitely coming from outside the vehicle and not from the speakers.
Any suggestions out there?

I find this post very interesting because I have the exact same problem.  I drive a 2001 Jeep Grand Cherokee 4.0.  Around November of last year I had this noise whenever I went above 20 and once I fell below 15/20 it would just quit.  It sounded like it came from the driver's side front (near the tire maybe).  I thought it was just something rubbing against the tire at first because I just had new tires put on.  Well the noise wouldn't do it all the time, just occasionally.  Well after about two to three weeks of this it came to a stop altogether.  All went well till just this past weekend.  It started doing it again, only this time it does it when I reach 30 mph.???  It progresses until I can't hear the noise anymore because of the highway noise.  Once I fall below 25/30 it quits.  Again it does it only occasionally, but when it starts it keeps doing it.  You can stop and start up and it will keep doing it.  Sometimes it will be above 30 and it won't be doing it, then all of a sudden out of nowhere it will begin??  I have no idea what it is, and frankly am a little afraid to take it to the dealer bc all they will do is drive it once and my luck it will be the time where it won't do it.  Did you ever find out what caused this problem, or does anyone have any suggestions??  I don't think it's the CV joint bc I can steer just fine and get no "clunking" noise when I turn.  There is a "popping" noise when I am coasting around 10 miles an hour, which seems like it stops/slows as the car slows down and speeds up as the car speed up.  Any suggestions on what this odd whinning noise is?  Anyone??  --Any help is appreciated.  Thanks Matt!  

I've got the exact same noise.  Really peeved at the moment, so I scoured the internet and on the 20 page of results from a Google search, I think I found it...This exact problem is described in a technical service bulletin issued by jeep.  Look at 0300101A on this site:

http://www.wjjeeps.com/tsb.htm  

Dont know if this helps, but had the exact same problem in my 95 jeep cherokee wagon and this loud whirring noise would only kick in at approx 50km/hr and get louder as I went faster (i'm from Aussie). It got louder when I turned left and quiter when I turned right.It ended up being the left wheel bearing. It thru my mechanic off because usually when a wheel bearing goes you should hear it all the time when the wheel rotates. I don't know about your model, but the wheel bearings are a sealed unit with the lockable hub and cost ***  

Sorry, should have posted a reply to this before now.  It turned out to be the wheel bearings in the left rear.  Fix was a complete new wheel hub and a new U joint.  Cost wasn't that bad to fix believe it or not.