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

 

Try to gain some more data about the problem before shipping it to the dealer unless you have got deep pockets.
What happens if you do the following when it's making the noise: A few ideas.

Put the trans in N or change gear
Cut the engine (take care).
Very lightly touch the brakes so the pads just rub on the discs.
Apply a heavy electrical load. e.g. Headlamps / rear screen.
Oscillate the steering slightly from side to side so as to move some of the vehicle weight from side to side.
Does the noise continue rather than abruptly stopping if you stop increasing / decrease speed. i.e. is the problem speed or time based.
Try applying a wide strip of duct tape across the top of the windscreen (from glass to metal across the full width of the car).
How repeatable is the problem? Does it always do it? Does it always come back when you slow down or only once you have stopped.
Has any work been done on the car at about the time this problem started?
Is the problem weather dependent?

 

The problem is repeatable, and seems to be somewhat weather related - it appears more during colder weather. However, there are days when it just doesn't happen at all, making it all the more confusing. The sound appears to be coming from under the front right quarter of the vehicle.

 

Hi,
You didn't provide additional data.
Without the answer to my questions and oany others you can think of its just a guess i the dark.
You say cold makes it worse. What about wet / dry .
Stuart

 

If you have central locking. it is possible that one of the vacuum elements has a leak in the door. The w202's sometimes make a noise just like you describe which is caused by a leaking vacuum element in the heating system.

Try locking the car while you drive and see if it changes.