My guess is it's your upper ball joint. You should be able to put your hand on it and feel for vibration as you bounce the car a bit, since it is higher than the tire. Just don't let the fender hurt your arm. I had the same problem with my 210. Mine were not worn but clearly out of lube, so I lubed them both with a grease needle. (My neighbor with a 211 just stopped the squeak on his lower ball joint using a grease needle.) My upper ball joint is above the grease boot so I had to bleed air so I could fill up the boot, and it took a few days to totally stop the squeak. I guess it took awhile for the grease to crawl up into the ball area.

__________________
'97 E 300 D