Mercedes Benz repair: Whistling noise between 30 mph-50 mph, police siren sound, vacuum test

Question
When starting cold I have a whistling noise between 30-50mph. The colder it is, especially lower than 40 gegrees outside the louder the whistling noise, almost as loud as a 90db police siren. Sound goes away after about 15 minutes of driving. Vacuum test under the hood was a steady 23hg. Fresh air valve? Sound is coming from lower dash area or else under car someplace. Hard to determine. Benz dealer can't figure it out.

Answer
Good morning Norm!
Sounds like you may have a slight crack in one of the hoses that goes to your air slide(air valve).
What you probably want to do is start the car with air cleaner removed and look and listen for sound.Get you a can of carb cleaner and start spraying it around the air valve and surrounding areas.MAKING SURE THAT YOU STAY AWAY FROM EXHAUST AND SPARKS! This should put you right on the whisle and it should go away for a brief moment.
This can be hard to find and is probably something simple that the dealer just overlooked.I dont know what model car you have but it should be the same on any Mercedes.
Also change your a/c and heat modes if you cant find it as it maybe under your dash and a vacuum valve could be leaking. By switching the a/c controls you may make the noise change and if it does, then you probably have a leak in there somewhere. Thanks and i hope this helps. Ricky