Guess why....
Worn out hub and bearing on the left side. I've never read or heard of this! Today I felt a vibration and heard a rumbling noise when turning to the right on the freeway. The LF wheel had more brake dust on it than the other 3. I lifted the corner by jacking it up from under the LCA and was able to wiggle the wheel quite a bit. My local NAPA had them in stock : $218 !
I guess this must be a common wear item for a store to have them in stock.