I posted this on the maseratiforum a while ago, not sure if it helps
I've just been looking through the collection of the Maserati Academy documents that have just been posted here
here One document (the 4200 wet sump engine overhaul training manual) explains how the cam variator is held in place (at rest) by a spring loaded locking pin.
here and full document here
http://www.scribd.com/doc/201140054/4200-Wet-Sump-Engine-Overhaul (what look like notes from the training course) explains that a rattle on start up can be caused by the pin not engaging
https://www.dropbox.com/s/jf640pxmcfrorr5/Dec-11-2014_11.51.47-CapturFiles.png?dl=0 So I guess the explanation on the wet sump (QP & GT autos) is that the spring forcing the locking pin into the cam variator at rest, gets gradually weaker over time and does not always lock the variator into place properly. Then when the engine is started you get the rattle because the variator can move as there is neither the locking pin, nor oil pressure to hold its position. This may explain why the rattle does not start until the cars are 3-4 years old, and why its intermittent as the spring weakens. IF thats correct, then the fix is a new spring - but getting to it is another story!
Has anyone had the noisy cam variators fixed at any of the Independants?
What sort of money/time has it taken? Best Regards, Jason