I test drove an '07 E320 Bluetec yesterday a doctor friend who is moving over seas (Egypt) is selling. At idle, the car sounds funny, like a sewing machine that makes a little ping irregularly popping up now and again. Although quieter than my idling E300, it doesn't sound as smooth.

I have never driven another bluetec, and didn't have the luxury of asking a salesman about the sound or if I could listen to another one--the MD didn't know anything about it and I didn't want to insult him so I didn't ask.

Anybody have one? Is this the way they sound? In the cabin and underway you hear nothing, btw, and the thing doesn't feel much faster than my chipped E300, but there is no discernible lag. The thing is mint and has 11K on it--blue with tan leather and a wood-trimmed steering wheel. Very good price.

Thanks.