Ok, there's some misconceptions, here, about how the dual mass works.
First, if the engine is missing, a dual mass flywheel in good condition will not rattle. But, the transmission will rattle.
Gear rattle from the ZF S6-40 six-speed, when the engine is idling, is the result of changes in engine speed caused by firing impulses. The engine fires four times per revolution. If you could very accurately measure engine speed, you'd find it fluctuates. A cylinder fires and the engine speeds up, but then slows before the next cyilnder fires. Then it speeds up and slows, until the next one fires and so forth and so on.
At idle, this fluctuation happens slow enough that it causes the main drive gear and the countershaft teeth to rattle against each other.
The dual mass flywheel damps some, but not all of that rattle. If the engine is missing, the fluctuations in engine speed are much greater and, thus, the rattle from the trans (in-spite of the dual-mass' damping) is louder.
When the dual mass flywheel fails, the damper weight may also begin to rattle and, because the dual mass is failing or has failed the gear rattle from the trans gets worse.
This problem is compounded in 89s, 90s, 91s and some 92s which have the earlier ZF unit having gears with teeth having less helix angle.
You can eliminate the expense and weight of the dual mass by going to a standard flywheel, typically an aluminum unit. This is a common performance upgrade, however, when you ditch the dual mass, you get an increase in gear rattle and also low rpm growl in first gear.
The best aluminum flywheels for replacement of dual mass flywheels are either the McLeod or the Fidanza. Those two, also, make the best clutches, IMO.
