Yikes. The U-joint would be a possibility; I wouldn't know how to tell if it was bad (I'd think the vibrations would be mostly under my butt, then, but I realize vibrations go wherever they feel like). As for the wheels, I recently had all four balanced and new tires put on the front ... if they were bent, do you think the tire shop would be able to detect that? That jumps out at me a bit because the tire shop I went to for years (including once a month ago) put the lugnuts on with way to much torque. I had another shop do the tires and put them on correctly, but I'm still worried the wheels or lugs were damaged. The vibrations came on gradually last winter, not at any time near having it at the tire shop, though.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)