Jeff,

Thanks for the reply. I checked a variety of things on the car this weekend and here is what I have found. Tire wear is normal, but pressures were off on all 4 wheels. *sigh*.
I re-set everything and went to work looking at the suspension (front and rear). All bushings in all the sway bars look good and are still pliable. There is no play on any of the bars. So, I pulled the front hub caps to get at the bearings, but the grease was in such good condition and the wheel appeared to be spinning in such good order that I left it alone for the moment. I went through checking brakes and rotors and changed the rear pads. All else was in good shape. Springs and shocks looked good and no bushing/seal cracks or wear wherever I could see.
The "thump" itself initially felt exactly like the toolbox in my trunk lifting up and dropping. (Of course, I took it out and this is not the cause...plus, I can now distinctly hear it coming from the front wheels.) The thump only occurs once each quick turn and only at the apex of the turn. This only started recently (2 weeks) and ONLY occurs when the turn I am taking is close to 90 degrees and is more than 10-15mph or so. Yielding and merging and slow turning produces no noise or vibration, at all.
After all the weekend checking and maintenance...the thump is still there, by the way.
Puzzled,
John