Some things to check:
1. Make sure the engine is cold. This is important.
2. Start engine and increase revs slowly to around 1500-1800 rpm and possibly up to 2200 rpm.
3. Listen for the rattle near the front of the engine.
4. Check again after engine is at regular operating temp.
If the rattle goes away after the engine is warm, then you need to get to your dealer right away. You have the dreaded "paint can rattle".
Mine and another Captain's Rocs are at the dealer right now. The other Roc had a catastrophic engine failure when the loose cam chain skipped a tooth ending up bending valves, etc. Luckily, I got mine in there before this happened.
I appears that there might be an increasing shortage of replacement cam chains. My dealer received all the parts to repair it (tensioner, guides, etc) except for the chain.
Triumph has been very gracious with covering this issue under warrenty even if yours has expired.