Those engines, even with the hood up are amazingly quiet...there is NO clatter. I just looked at one of the new Bluetec engines and listened to it with the hood up and couldn't tell it was a diesel. The salesman didn't even know it was a V6 as opposed to the CDI I-6, so I taught him a few things.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

You need to take off the engine cover. There's a giant foam blanket that helps to muffle the clatter (it can also gets ruined when the high pressure rail develops leaks).

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

That's weird. The video linked below has some samples of a bluetec idling with the hood up. Much to my relief, these engines still have a very healthy diesel clatter. I don't know why you couldn't hear it.
http://youtube.com/watch?v=M9Iki0-3_YI

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL