I know of it happening a few times. There are a number of other causes also - gear chatter seems to be VERY prominent in some examples (mine) - also had a p/steer pulley out of line that started to shred the belt, which made a similar noise. The fact that it happens on idle though, could be gear chatter.. it's really quite loud.
The series 2 has the L77 in manual or auto and has the AFM/DoD in the engine. It is just disabled in the manuals. I have done 8000+km so far and it is quite noisy at times. I'm hoping that some decent oil instead of whatever holden put in will fix it.
One differences between L77 and L76 is that the L77 does not have the DOD lifters like in the L76 AFM cars. The DOD lifters are designed to blead down when AFM mode is activated. They can made a slight chatter when pumping back up but normally for only a 2 ro 3 seconds. The L76 has 4 DOD lifters and 4 normal.
Not realy hearing the nosie your suffering from and for how long it goes for makes it hard to pin point. Maybe upload a sound or video file of the noise. Is it worse when the engine is hot or cold (such as first startup). I have had 3 engines relpaced in my ssv to rectify startup rattle (sounded like a captiva) till the one I have now (later model L98) seems ok. However my issues might not be the same as yours.
From what I have been advised, these engines should not make any abnomal ratteling, clucking, deisel engine type noises at all. I would persist with getting it looked at quickly an don't take the "thats normal" explanation. We have many of theses cars in our fleet and I tested 7 and none made the noise mine did.
P.S. Changing your oil probably wont fix the issue (it may mask it) so save your money - I spent lots of money doing the same thing
i just sent in my 6 litre 08 stato last monday (a week ago) with a rattling noise that sounded like a lifter - aparently i have a screwed cam shaft?!?! and that particular part has to come from america? he said it is on back order?!?! i thought statesman were 100% aussie made down to even the motor....hmm i smell something fishy he has had my car a week now and its depressing driving the missus's astra