Hi aarden,
I have the same issue and have had it in to 2 garages....if it's only ticking under acceleration I would say it's Pinking...same problem as mine!
Running 98 helps slightly, but does not get rid of the problem. I have been advised to retard the timing as this may solve the problem? I'm booking it in for a reflash and dyno at the end of Nov. so I'll let you know!
Other solutions that have been put to me are changing the plugs...
Unfortunate thing, is none of this is covered under my warranty!!! I have mechanical cover, but not electrical..
If you do get a fix, keep me updated!
Cheers