While coasting around 60MPH, my 84 300SD W126 emits a sound from underneath which is similar to a bell. A continuous bell sound and not pulsating. The sound is noticed above 50MPH and does not change pitch when speed is increased to 75MPH. Not noticeable on low speeds. Just wondering if any members had experienced this.

I have seen(heard) this happen on other MBs. If it is sort of a high pitched noise, then I suspect you may have a bad mid-shaft bearing.They are not expensive. The bearing is $12.00. If this is your problem, and you have to replace the bearing, you might as well replace the mid-shaft support since the bearing fits inside of it. The support costs about $22.00.
Bill Lewallen Lexington,Ky.