Today I finally got to work on the car. Based on all the advice here (and the fact I couldn't find anything else wrong however hard I looked), I changed the front rotors - and fixed the problem.

I will say that the rotors didn't look that bad at all; but I did notice the inner 1/2" on one side of one rotor was clearly not polished to the same degree as the rest; I'm guessing it may have been corroded there before the new pads went in.

Many thanks to everyone for their advice....

-Steve