UPDATE: I finally had time to take the Jeep back to the shop, and it seems that the bearing in the kit (I bought a complete axle kit that included the seals, alloy shafts, ARB lockers, ring and pinion, and basically everything else inside the axle) was bad, and it got damaged, allowing some play in the pinion. This caused not only the whine, but also the vibration at high-speed (65+ mph). The bearing looked burned off for some reason.
The good news is that the shop honored the warranty, and put in a new bearing, as well as new ring and pinion (because of the play, the old ones were done for). Now the Jeep has no noise (well, none that it did not have before anyway!).
As for the front axle, they also replaced the front seals, and now there is no leak. So all is good now. Finally got stronger axles (yeah, I know, I still got a D35, but I should be OK even when the 33's go in, as I will not see that many rocks; mostly it will be mud) and lockers working properly. I only need to get around to changing the U-Joints and reinstalling the front axle (will probably do so this weekend) and I am done with the drive trail!
Felipe