Bad front sway bar end links are common on this model, but they make more of a knocking noise at low speed <35 mph. I wouldn't call it a squeak.

I'd get three friends in the car, roll down all the windows, and have them listen. At least that way you can determine whether it is coming from front or rear, and perhaps narrow it down to which corner of the car.

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'98 E300 turbodiesel