Originally Posted by AzNMpower32 (Post 862670)

The cetane level makes a substantial difference. My dad was b*tching about the same thing. Then I introduced him to the concept of higher cetane diesel fuel, which is available at some locations but it varies by state. Once we started putting in premium diesel fuel (45-47+ cetane), the clattering went away, and the engine output is both smoother and quieter especially along the highway. This has proved consistent over many months and tankfuls of varying types of diesel fuel.

In Europe, under DIN EN590 the minimum cetane level of diesel sold is 51 and thus most diesel engines including the BMW ones are designed to provide optimum performance at that level. In the US, the minimum and most common cetane number is 40; modern diesel engines will compensate for that and the behaviour is what you're experiencing. Labeling laws vary by state. My dad lives in VA: Law requires the cetane to be posted and thus, one can distinguish the difference.

Long story short: what you're experience is a result of the lower cetane diesel. The fix? Find premium diesel, which may not be available in your state. If that's the case, well, you're SOL.

Originally Posted by JCL (Post 862655)

You will always have additional noise with the diesel, and there isn't a way to get rid of it (except, as others have said, buy a gasoline engine instead). The noise is much less than with older generations of diesels due to the multiple injection events and better managed combustion process.

I would be interested, however, in whether it has changed while you have owned the vehicle. If not, then there is not much to do about it. You can tolerate it (thinking always about the fuel economy), or you can celebrate it (imagining that you are driving a heavy truck). Both approaches have been described here by different posters, and posters who are fans of the diesel tend to fall into one of those two camps.

If it has changed, I would look into the fuel quality I was buying (cetane number) and see if different fuels from different suppliers had any impact on the noise upon acceleration. The cetaine rating describes how the diesel ignites, and low cetane numbers will increase engine noise. Not all diesel fuel is the same. Cetane isn't the same as octane rating, but it is somewhat similar in concept.

I don't think there is any significant difference between the 335d and X5 35d in North America since they both use the M57 engine. If you are comparing a new model (overseas) of the 335d, then you could be comparing the newer N57 engine to the older M57 engine, and I would expect them to have different sound levels.

Originally Posted by LeftCoastErik (Post 862682)

I'll chime in here. I just got my 2012 X5 35d and I am very happy so far. The "rattle" you hear off idle is actually timing rattle and pretty common on most HPCR diesels. I own Left Coast Diesel, and we do everything from oil changes to competition builds on diesel pickups. My other truck is a 675rwhp 2004 Ram diesel and it does this pretty badly with the larger injectors and programming I have in it.. anyway, as timing is increased, especially at low rpm/high load condition (like off idle or tip-in at cruise) you will get some rattle as the rpms increase to match the timing in the map.
Hope this helps some.

Originally Posted by LeftCoastErik (Post 862705)

I imagine, in typical BMW fashion, that our DMEs are pretty complicated.

Originally Posted by diesaroo (Post 862679)

Right, similar in that octane and cetane are both "good" for gasoline and diesel engines respectively, but for opposite reasons. High octane = large ignition delay to avoid pre-detonation. High cetane = short ignition delay to start the burn early for more complete combustion...longer burn duration...less bang.

Originally Posted by LeftCoastErik (Post 862682)

I'll chime in here. I just got my 2012 X5 35d and I am very happy so far. The "rattle" you hear off idle is actually timing rattle and pretty common on most HPCR diesels. I own Left Coast Diesel, and we do everything from oil changes to competition builds on diesel pickups. My other truck is a 675rwhp 2004 Ram diesel and it does this pretty badly with the larger injectors and programming I have in it.. anyway, as timing is increased, especially at low rpm/high load condition (like off idle or tip-in at cruise) you will get some rattle as the rpms increase to match the timing in the map.
Hope this helps some.