I had the same problem with my 2010 STR and basically it is a stuck cam chain tensioner. I replaced it with a manual A.P.E cam chain tensioner that only requires maybe a 1mm adjustment every 10,000 miles. I haven't needed to adjust it yet. Triumph went to a hydraulic tensioner in 2011 I believe. To fix the stuck tensioner;

-Remove the cam chain engine cover.
-Wedge the guide with a suitably sized socket between the guide and engine case.
-Remove the tensioner center bolt and spring.
-Remove the other two bolts and withdraw the tensioner without disturbing the plunger.
-Measure the distance between the tensioner body and the bottom of the plunger (mine was around 7 mm).
-Pull on the plunger to advance it one notch past the as found setting (mine was now 8 mm) you can lift the ratchet clip to push the plunger back if you go too far.
-Smear some grease on the tensioner O-ring and put tensioner body back in and tighten the two bolts (do not over-tighten).
-Replace the spring and center bolt.
-Remove wedge.
-Use a drop of aviation gasket cement if cover gasket broke and reuse gasket if you don't have a new one.

If you still hear cam chain noise on cold start-up which may go away as it warms then repeat procedure and advance another notch. Usually 1 or 2 mm adjustment cures the problem but if the tensioner sticks once then it may stick again. Manual cam chain tensioners are available for many Japanese sport-bikes too so it is a common problem. Do not adjust more than 2 mm or the cam chain may be too tight and the ratchet may slip resulting in a very loud and loose cam chain while riding.

 

Thanks for your reply. Will take the CCT out to have a closer look one of these days.

 

It's very normal for you to hear a little chain rattle for a few seconds when firing up a cold motor in the morning. As long as the rattle goes away after few seconds, I would not be concerned. Now if it goes on and/or you start hearing it under power - then you need to consider either changing it or swapping to a manual adjuster.

 

As I wrote in the first post the rattle goes away after about 20seconds upon startup, but there is a rythmic rattle/ticking especially at low revs. Will check behind the engine cam chain cover