Judging by the details you provided, I can definitely tell you that your problem is bent wheel(s). Have your mechanic carefully run your wheels on that balancing machine and check for such a defect.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver