Backlash
Many of the earlier rockets have what is called a "paint can rattle" after reving to 1500-2000 rpm and then releasing throttle. Many threads on both websites (r3owners.com and .net) have been written on this and you can check these to determine if this is similiar to what you are experiencing. Mine (07) has a similiar sound when first started but goes away when warmed up. I understand if the noise goes away after warmup there is no problem. If it continues after warmup it is a major problem.
Do you captains with more experience than I agree? At any rate, Triumph has always stepped up to the plate and corrected the problem as I understand, but you may be without the bike for several weeks. The bike is a great bike and Triumph is a great company, I hope your dealer is good because most of the time the dealer is the problem. In my observation the three others that have responded to your question know more about the rocket III than many dealers (look at the number of their posts), so would go with their advice.
Good luck and welcome.
rider