I have a 2001 e320 4matic wagon that has started to develop a high frequency vibration when the car is running around 40 MPH and I let off the gas. The vibration is a higher frequency then you would experience from an out of balanced tire. The tires are about 70% worn. Is it possible that asymmetrical tire diameter is causing the vibration?

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1999 S320
2001 E320 wagon