Rear end wobble

[Helium2]

2010 SL AWD 65,000 mi.

Occasionally at 65-75 mph I experience some shimmy as if a tire's out of balance, but it never lasts more than a few minutes and doesn't often repeat.
Last week, when gradually slowing down from 65+mph I experienced a severe wobble that seems to originate from the rear as the steering wheel doesn't move but the seat does.
This happened at about 45 mph and went away at about 30 mph.
Then there was a repeat wobble as I came to a stop.
This has not happened since.
Thinking back I remember a occasional wobble at low speeds, usually as I was slowing down, but it happens only infrequently.

What the heck?

[Rogue Jarhead]

Things that make the rear end wobble.

1. Loose lug nuts.

2. Unbalanced rear wheel

3. Loose axle nut. That's the big nut in the center of the wheel.

4. Worn rear bushings.

5. Warped rotors, they usually show up more as a shake when you apply the brakes.

[Helium2]

Checked lug nuts.
Unbalanced wheel would show up all the time.
Warped rotors would show up all the time.
So that leaves:
Wheels seem tight but haven't jacked up the car to see what they're like with no load, yet.
Are you talking about suspension bushings?

[Rogue Jarhead]

Yes suspension bushings. Warped rotors only wobble when you apply your brakes. Is it possible the axle nut is loose? I had to replace a rear wheel bearing once and had a hard time getting the axle nut to stay tight. I knew it was coming loose again when I would go around a curve and the rear end would wobble.

[ImStricken06]

wheel or rotor not 100% flush against its seat.
control arms are worn (bushings)
rear cv axles could have issues.