I have a few idea's, but you never reported back after this thread........ 3 months ago??Our 95 E320 wagon has begun to make a new noise. The noise is a very low pitched sound -- almost sounds like a subwoofer at 30hz. No grinding, just a smooth very low frequency tone. The sound only appears while on the freeway at 50+ miles per hour when LETTING OFF THE GAS. It is loudest when doing this at 70+ mph. The very second I engage acceleration, the sound completely disappears. Any ideas? Drive shaft? Rear diff? Trans?