The hum is gone. I got back under there and removed and reset the front driveshaft. My best guess is that in my first attempt I tightened down the 46mm nut before the driveshaft reached its equilibrium length(or "settled" if that's the term), somehow causing it to bind along the way. Anyway, after resetting it, I drove at high speeds today and the car was very smooth and fun to drive. Thanks for all your comments.

Rich Mayer
82 500 SL