michakaveli,

I get a noise that fits the description you gave, and traced it to the enclosure panels under the engine. The noise would start when I got near 60 or so mph, especially in a cross wind. It sounded exactly like it was coming from those vents in the hood.

I read somewhere in a post on this site that the vents themselves have undergone a design modification to address noises. I mentioned this to the service guys at the local dealership and they did not seem to know anything about such a design change. But they did fix the noise by re-fastening the panel under the engine. Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)