Hmm.. The beginings of this thread are actually older than the length of time I've had my car (Since September). I bought my car used at about 20k miles. At 24k miles I started to hear clunking on the outside of the rear driver side wheel/axle area, more promenent when going over speed bumps, but also audible on slight accel/decel. I first thought it may have been brakes and not under warrantee, so upon inspection I found the large axle nut which holds the half-axle to the wheel hub had come loose, and backed out all thw way to the cotter pin! I was actually able to slide the whole axle about 1/8" in-and-out from the wheel hub in the state it was found, while the axle nut had been backed out about 4 turns 'natually' over time.
I fixed it myself since I was right there, in the garage, with some tools available. The axle nut is about 1.25" in diameter...
All I did to fix was first clean the area a from some of the grit/grease globs, pack in a bit of greese as best I could, and then re-torque the axle nut with a new locking sleve and cotter pin. The car is now at 33k miles and makes no noise at all.
More notes on this; Nissan did include a cotter pin, but from the looks of it did NOT design the axle nut to be locked in place by a cotter pin. Usually axle nuts have slits ot holes in them, or in other designs I've seen are something like this:
On my car, a standard cotter pin is in association with a standard nut on the axle; meaning theres no way the axle nut can be kept from loosening up about 4 full turns before finally beig stopped by the cotter pin.
My car's axle nut looked like THIS, without splines for locking with the stock cotter-pin.
Also the natural forward roll and rotation of the assembly could cause the Axle nutt to back out as well, as it is of regular and not reversed thread pattern. I could only speculate, but I bet the passenger side does not have this issue as forward rotation should tend to keep the assembly TIGHT.