I have the same squeak, but in my RIGHT rear tire side, not left rear.
And yea my car is lowered with eibach rear sway bar with figs bushings and endlinks, and figs rear toe links, but it's had this setup for months now. And the squeak is kind of new.
I only notice it when I enter my driveway, meaning the car dips down, then up again.
I don't notice it when I exit my driveway, which is weird.
any ideas? could this be a bad rear lower ball joint? is it common to have to buy new rear LBJ's?
or is it the rear subframe mounts like posted above?