I can only see a rubber plug looking thing on my rear differential, not a pipe plug. Jeep grnd chrkee 99. Got any ideas on how to remove it and then replace it?

On the rear differential there will either be a metal plug or a rubber plug. The metal plug can be removed with a 3/8-inch drive ratchet. the rubber plug can be removed with a small screwdriver. Faceing the axle from the rear will see the plug to the right side on the cover plate. Remember to also check the front differential as well. Hope this will help you.

If there is not a plug on the back cover then there is a plug on either the drivers side or passenger side just behind where the drive shaft attaches. Make sure you put enough in it or until it starts to overflow out of the fill hole.

it is just one plug, it is locted on the side of nose of the differential, it is pipe plug

How to Fill a Rear Differential
You may need to add fluid to your differential due to leaks or changing seals, or it may be time to change out the gear oil completely. Either way, it's just a few steps to fill the rear differential and get your vehicle back out on the road!This article will explain how to fill a rear differential. jQuery('.intro .thumbnail').each(function(i,e){ jQuery(e).find('img').one('error',function(){ jQuery(e).remove(); }); }); Difficulty: Moderate
Instructions and Things You'll Need:

• 3/8 inch drive ratchet with extension
• 2 quarts gear oil (gear lube, differential fluid)
• Side cutters
• Oil drain pan
• Shop rags
• Flashlight or shop light (optional)
• Lock tight (optional)

Filling a Rear Differential

1. Be sure the car is raised on four jack stands and is level. It will be more difficult to fill the differential if you've only got it raised in the rear.
   
2. Place an oil drain pan underneath the plug to catch any leaks or drips. Keep shop rags handy for any spills.
   
3. Check your service manual for the amount of fluid your differential needs, if you're completely refilling the system. Two quarts should be enough in most cases.
   
4. Remove the spouts on the gear oil containers. Peel off seals, then replace spouts. Use side cutters (or any cutting tool you've got handy) to clip off the top of each spout.
5. Remove the differential fill plug using a 3/8 inch drive ratchet with extension. (Some models may require a hex key or screwdriver, but the 3/8 inch is the most common plug design.)
6. Take the gear oil container and fit the spout into the fill hole. Pour the fluid inside. You can gently squeeze the bottle to speed the process. Repeat with a second bottle if necessary.
7. Fill the differential until the fluid starts draining back out of the hole.
   
8. Clean and replace fill plug. Use lock tight (thread locker) to help seal if desired. You can see my eHow article "How to Replace Rear Differential Fill Plug" (video) for more information.
   
9. Take the car for a drive around the block to get the gear oil moving. When you return, check underneath for any leaks from the fill plug or differential cover.
   

Hope help with this.

All differentials have a provision to check that. Usually you will find a rubber plug in the cover or a access port in the housing with a male or female 1/2" wrench attachment provision. (basically a pipe plug) Always check on level ground. Fluid should be just at or slightly below the hole.(use your finger or a pencil as a dipstick.)

in most cases the filler plug can be reused, but if it is cracked looking then replace it, they are very cheap, u must buy them from the dealer.

check the differential fluid in the rear differential. if the fluid is low, add fluid and see if the noise is still there, if the fluid level is ok see if the fluid appears metallic, if it is metallic looking or excessively thick it would be a good idea to have the bearings checked out. i am in the process of rebuilding a front differential on a 98 jeep grand cherokee for the same problem. the bearings inside the differential on the carrier and pinion gear were worn out causing a humming noise. if the wear is excessive the gears might also need to be replaced

If you can drive normally without losing power, it does sound like the rear differential. If you push the gas down and it seems like you don't move as much as you should, it could be the transmission. From your friends description it sounds like the rear diff though.

Shop around.

There's a few more things to check out:
1. The track bar links, which attach from frame to the sway bar. Inspect the bolts/nuts to ensure they are really tight and the rubber isn't worn to the point of slack.
2. The bushings where the upper control arm attach to the frame. Inspect these for torn rubber/missing bolts. (These 2 bushings are on the fore end of the wishbone where you changed the upper ball joint.)
3. The bushings in the other, straight control arms that restrain the differential.
4. The shock absorber bolts/rubbers at frame and axle.
5. The u-joints on drive shaft.
6. The differential input pinion bearings. Raise vehicle and really yank/pry/push around the drive shaft and look for any slack.
7. The drive shaft at transmission. Check for any play over 0.020", side to side, up and down.
8. The transmission rubber mount.
9. The axle bearings. To check these, lift under axle, each wheel, and yank wheel fore/aft, up/down, and maybe use a pry bar. You're looking for axle bearing wear where the axle is supported at the outer ends of the axle tubes, just behind the brake mountings.
10. While the vehicle is raised (wheels off ground), chock the front wheels, and put transmission in neutral. Now check for significant slack when you manually rotate the wheels by hand, back and forth. If slack here (say, 10-15 degrees of fore/aft rotation on a wheel), then the spider gears are probably worn at the cross shaft in the differential carrier. Depending on the amount of slack, you can change the spider gears, side gears, cross shaft, and the associated thrust washers yourself, if you're a capable mechanic. This requires opening the differential cover, removing the rear axles (at least far enough to get the axles out from the side gears), remove the cross pin retainer bolt, manipulate the cross shaft out, manipulate the spider gears with their thrust washers, out, manipulate the side gears, with their thrust washers, out, then replace the above, with a 'gear kit', which includes the side gears, new thrust washer, spider gears, with new thrust washers, cross pin, and cross pin retainer. A 'gear kit' is around $85 for the Dana 44, 30-spline axle kit. While those parts are out, pry the carrier in each direction inspecting for slack in the carrier bearings and check the pinion/ring gear slack at that time. If you find a bad carrier bearing or pinion bearing, then you should probably find a mechanic to replace those, unless you're a 'very capable' mechanic. After reassembling the gear kit (side gears with their respective thrust washers, spider gears, with their respective thrust washers), cross pin, and retainer bolt, clean the sealing mating surface of both the axle housing and cover, remove the fill plug from the cover, apply RTV sealer to the cover (1/4" bead), attach the cover with bolts, replacing the tags in their original locations, refill differential with either 85w oil or 70W140 synthetic, as desired, approx 2.3 liters, replace plug, and check for leaks. Note: when removing the differential cover, remove all but 2 mid-side bolts, and make them loose. Then tap the very bottom of the lid towards the rear to loosen the cover, have drain pan under the differential to catch the oil. Then remove the 2 remaining bolts and cover. The lid projects below the housing about 1/16" and that is the part of the lid you want to bump on to loosen the cover.
11. Rear disc brake caliper mounting brackets.
12. The sway bar rubber mountings on the axle.

.. and that pretty much covers everything that can make noise on/in the rear end.

13. If a tow hitch is attached, check that for proper attachment.
14.Fuel tank loose, or fuel pump inside tank loose.
15. Spare tire loose, or junk in the spare tire carrier hole.
16. Loose junk in the right rear side compartment (this is actually a CD changer compartment, but if no CD changer is installed, then people put all kinds of junk in there)
17. Rear lift door. Open it a bit and check for side to side play. I've heard of terrible noise on my rear lift gate, and it was the rubber wind seal making a bunch of noise. I wiped it with a rag I sprayed silicone oil onto and quieted that down.