Could be the tires are out of round. And or they could be starting to cup.I had both CV axles and Intermediate replaced a few months ago and I still get a vibration noticeable after 55MPH. Its a rhythmic whoop-whoop or like a thuuuump thuuuump sound. Had tires balanced and rotated to rule that out. Rear u-joint and front driveshaft both replaced 26K miles ago, new upper and lower ball joints 11K miles ago. I stopped letting it drive me crazy (because it was driving me nuts) and just turn up the radio on the highway.
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