2011 335i Convertible. Around 4k miles I started to develop a pronounced grunting or groaning sound when slowing toward stop-lights. When I first brought it in, my SA pulled the shop foreman out to hear the sound. Prior to even saying "Hello" he said: "Well, I don't think it's a waste gate issue." That was the giveaway (wishful thinking on the part of the foreman). They first reported "sand and gravel caught between the exhaust heat shielding and chassis." They "fixed" it by bending the shielding. Of course, as soon as I drove it home from the shop, the sound developed again. I brought it in again, and my SA told me it was probably a turbo waste gate issue. They had the car for three days checking all systems leading up to the waste gates. Finding those in order, they "adjusted" (I couldn't get any more info out of my SA) the gates and pronounced it fixed. I just picked it up at lunch time. The most immediate thing I noticed was the turbo hesitates a little now and bucks a bit when it kicks in. The drive home tonight will tell if the problem's gone. So these N54/N55 waste gate problems sound fairly common. Anyone with a similar issue? How'd it work out for you?