It sounds to me like a ball joint has run out of lube. Since there are likely no grease fittings on yours, replacement is the normal fix. If you drive it long enough to get the squeak going good, you should be able to look under the motionless but running car while someone turns the steering back and forth, and hear which side it is coming from. feeling the ball joints while it squeaks should tell you whether it is the upper or lower, assuming your car has upper ball joints.

If you are DIY experienced, it is possible to determine if the ball joint is worn, and if it is not, grease can be injected through the rubber boot using a grease needle to give a good but dried out ball joint another lease on life.

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'97 E 300 D