JOP- DO you have the Cat 6 speed box?
Regardless, does putting the clutch (even if you're in neutral...no load) in kill the rattle?
I say all this, because I have the 6 with a lightweight flywheel and my box rattles a lot when you have the clutch out and are in neutral. So much so that my very experienced mechanic (though not necessarily with Se7ens...he only services one other) didn't want me to drive it at the Dragon. But a quick search on BlatChat (the UK club site) revealed that TADT="they all do that". Especially apparently if you have a lightweight flywheel. Scott L. had a similar rattle and I think they wanted to take apart his gearbox.
When I was down at the Dragon, I left my car idling and some of the guys asked me "What the hell is wrong with your car?" Seth of BAM (Canada), asked about the flywheel, and when I told him I have a lightweight one, he said..."Yeah, that's typical."
That said, check your gearbox fluid too.
Oh, and welcome aboard. I certainly hope this thread's not your last.:thumbs: