I started hearing a low whine from the rear end while driving on the freeway and it appears to be getting slightly louder. It sounds like it is coming from the right rear but I cannot be sure. There is no noise when I coast or if I am very light on the gas, it just exists under acceleration or normal driving. I decided to replace all of the fluids - front/rear diff, transfer case, and transmission, but it did not make a difference. I did notice that the right side of the rear axle has oily dirt on the bottom half of the axle (only on the right side near the wheel).

It also appears to take on a different tone around 10-20 mph (more of a groan than an whine)-not sure if this is a different problem

I am not sure if a wheel bearing needs to be replaced or something else.
Any ideas would be appreciated.

Thanks

When you serviced the rear diff, what color was the fluid, besides the magnetic mud on the drain plug, were there any metal chunks?

Well could be your hub. Jack up the rear and give the tires a spin see if you can feel some looseness. Sounds like in the least you have a gear oil leak.

The fluid from the rear diff was pretty black - all of the others were dark amber. Yes there was a lot of sludge caked onto the plug, but just a few (5-10) metal filings stuck to the magnet. This was the first time I changed the fluid - usually took it to the dealer - so I am not sure what it should normally look like.
Also I changed the fluid about 2 weeks ago and I still periodically smell it when I walk around the car after a drive.

You are smelling it because you have either a hub or outer hub o-ring leaking.
You need to deal with this ASAP, if it is the hub bearing failing, you can damage your axle, if it were just an outer seal leaking, a bottle of White Shepherd will stop the leak.
Since you have a noise, it is probably safe to say it is a failing hub bearing, which, with time, will also thru the 3 Amigos to come on and cost you at least $100 to turn off.

you'll damage more than your axle if you're driving down the road and a wheel bearing seizes up, there's a good chance you'll end up in the ditch

3 Amigos are already there - Thanks very much for the quick response. I have been browsing for parts - is there a wheel bearing that you can buy (normal $20 on most cars but I can't find it anywhere) or do you need to buy the whole assy (~$500)?

Thanks
Shawn

Hah $20 bearing! you wish, you have a DII and you cannot expect to just replace the bearings you need to replace the entire hub assembly. You are talking big bucks at a garage as they go for $500 new each plus a few hours labor. I bought mine used and put it in myself. All joking asides not sure why landrover thought it was good idea to put non greasable bearings on these things, stupid.

time for you to learn the most hated phrase in automotive history....unit bearing

Correction...sealed for life.

If you had a DI then $40 in bearings and grease and you'd be back on the road...but you have a DII.
www.roverlandparts.com
www.autosportsunlimited.com
Stop driving this truck until you can fix it.
If that bearing locks up on you and the road is slippery you will be in the ditch on your roof.