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It could be the timing chain , or it could be the tensioner itself .... it could also be the clutch ... if you notice the noise , then pull in the clutch (while running) and you notice a difference in sound , but the same kind of sound , it could be the clutch basket rattling ....
Usually the timing chain stretches after a large amount of time , or if the engine was overheated or run low on oil .....can they just go bad ?? , yes , but it does not sound like you have a bunch of hours on it , so my next guess would be the tensioner itself , they do go bad , and they will allow the timing chain to chatter .... so that is what I would look at first , if the clutch test fails to show anything ......
There should be 2 adjusters on that bike , one at the back of the cylinder on the shifter side , and the other on the head on the same side , the one on the head is the fine adjustment , so I would try that one first , if the noise stops or changes when you move the screw , then you will know if it is the chain/tensioner , if you adjust it and set it and the noise stays away , then you should be fine ...
Here is a video that will walk you thru the procedure ...
