I have a 2005 E320 that has a noise that sounds like a muffled “card in the spokes of a bicycle wheel” It seems to be coming from under the shift console and it only happens when the drive shaft is engage. It speeds up when the car speeds up and down when the car slows down. It is not heard when the car is in neutral even if the car is moving.
The first thing I would do is a visual inspection of the drive shaft(s). If you ended up with something wrapped around it, you wouldn’t be the first: http://blog.cardomain.com/2008/12/17/heres-why-you-should-never-run-over-a-mattress/
I doubt that you drove over a mattress - but there’s plenty of debris out there.