1999 E55 Exhaust or Intake System Resonance
 

My E55 makes a sound identical to what you hear when blowing across the top of a soft drink bottle. It occurs when driving down the highway between 60 and 70 mph and I gently press the gas pedal down to increase speed slightly. The sound is loud enough to hear over the radio and gets quite annoying after about 20-30 minutes of driving. I have had the dealer look at the car five times over the last 6 months and they have replaced all exhaust components from the driver's seat to the rear. We have also driven the car with the air cleaner removed, no change. I have taken the shop foreman, the service manager, and the area MB tech rep for rides and they all agreed it was not right until the tech rep said he drove two other 1999 E55s and said they did the same thing. So, it isn't a problem anymore and the dealer said they can't do anything about it.
Has anybody else had this noise problem? The car has only 32,000 miles on it, but I have had this problem since I bought it with 24,000 miles.

I am by no means implying that this is your problem but, VW's of recent years had a similar sounding problem.
Trouble was, some of the cars did not have all the body plugs installed, and under some conditions/speeds would exhibit funny noises.
I would think, if it sounds like blowing over a bottle top, the source could be of similar origin. ;)