C43 Owner Reports Heat-Related Vibration That Stumps Mechanic

A Mercedes C43 owner is seeking help after experiencing a puzzling vibration that has so far defied diagnosis. The issue, described as feeling like a 1990s diesel tractor, occurs only after the car is heat-soaked, typically following about an hour of highway driving, and does not happen every time.

The vibration is felt through the floor, not the wheels, and turning does not change it. Lifting off the throttle completely stops the noise, while reapplying the throttle changes the vibration in proportion to acceleration. Interestingly, exiting the highway and coming to a stop often resolves the issue immediately.

The owner is confident the problem is not tire-related, and downshifting during the vibration does not alter it, which rules out transmission or gearbox issues in their mind. They suspect a flex disk or driveshaft, but a visual inspection by a mechanic found no visible problems.

The owner wonders if a bearing might be losing grease properties when hot, causing the intermittent nature.

An AI suggested the transfer case as a possible culprit, but the owner admits to only basic mechanical knowledge. They avoided going to a main dealer out of fear of being charged without a solution, as the mechanic has been unable to replicate the issue while in the car. The owner is open to any suggestions from the community.