I have a 99 ML320 with 110K miles that has generally given good service. About 2 weeks ago it developed what I can best describe as an intermittent high-pitched whistling sound from the drivetrain. I've poked around a bit and cannot see anything obvious. It's hard to locate the noise exactly, and you cannot hear it as a pedestrian when the car passes. The noise starts only after the car warms up, it is definitely related to vehicle speed rather than engine speed, and is unaffected by applying the brakes. The noise starts at about 35MPH. Initially I made it go away my driving a bit in lowrange, but that now has no effect. It sounds like a bearing, but where?
Thoughts?