Troubleshooting a Rear-End Flutter Noise in a Mercedes

A Mercedes owner is seeking advice about a speed-related fluttering noise coming from the rear of their car. The sound first appeared in the spring or winter and becomes more noticeable when the rear seats are folded flat. It starts around 30 mph and increases in frequency and volume with vehicle speed, but not with engine rpm.

The noise remains the same whether coasting, cruising, or accelerating, and is unaffected by suspension loading over road contours.

The owner has already performed several checks. With the rear end on jack stands, neither wheel could be moved or shaken to produce noise, though the parking brake was left engaged. Tire tread wear was even, with no bulging sidewalls or wheel damage. No fluid leaks or damage were found around the axle connections to the differential or wheel hubs.

Swapping the left and right wheels made no difference.

The owner is asking for further troubleshooting ideas that can be done at home, such as repeating the play test with the parking brake off. They wonder if running the car in gear with all four tires off the ground, using two extra jack stands, would help, despite possible engine and exhaust noise.

An automotive stethoscope is available, though using it on rotating parts may be tricky. They also note they lack a GoPro, so having someone follow closely to observe the rear visually is not currently possible.