I have a 1981 240D which has recently begun making a whistling or whining sound. It increases in volume and pitch as the speed of the vehicle increases, but does not seem to be related to the engine speed. Once it reaches a certain pitch, it disappears instantly, but will start over and repeat the entire volume/pitch increase about 3 times. This seems to only be obvious at speeds below 55 miles per hour. This is a standard transmission. I have difficulty telling if it is actually a whistle, such as one created by air movement, or a whine that might possibly be created by metal on metal. It appears to be coming from the front half of the vehicle, and possibly more on the right side than the left. The vehicle has approximately 180,00 miles on it. Any thoughts at all before I submit this to an obviously expensive diagnostic session at the shop??

Thanks in advance