Today my wife noticed she heard water running on the passenger side everytime she came to a stop. I noticed too and came to the conclusion it could only be caught up somehow inside the lower chassis 'beam' on the right side. After prying in a certain rubber-grommet-like thing with my finger, out came a lot of water! See the pic, I marked the rubber with a red arrow. There's one up front on each side of the car as well. Are these vents/drains for the chassis? If so they might have clogged up over time. Fortunatly the water was crystal-clear! If it were rusty I really would have been worried now...

 

sounds like your drainage holes are clogged. trust me this is a BAD NEWS. sitting water = rust. you can't tell anything by the color of the water. that's a very common place for W210s to develop rust. goodluck..

 

guess we all should check them then. we've had a lot of snow and ice here in new england this week; first thing after i get the car washed will be to poke around and see if mine are clogged too.

 

The car has been standing still for over 2.5 years inside a showroom when we bought it, and we drive it for a month now so I'm not worried. We only started to notice the water-sound last week so it must have gotten inthere from washing the car weekly. I'm sure it hasn't been there for long and all that matters now is making sure those drainage holes are open...