I think it's a "German" thing. My 92 400e has a growl to it at idle. After having grown up in Mercedes diesels I wouldn't say it sounds diesel like - but certainly a bit aggressive. I like it, I think it adds character to the product. My wife's 92 Q45 - though a great car - lacks this kind of "vibe". I noticed that my cousin's '89 928 Porsche has a terriffic growl at idle. Anyhow its an asthetic I like about my MBZ - the overly stiff throttle (another "German" thing) I can do without.