I was thinking tensioners too. If you took your cam chain tensioners apart did you put them back together correctly? If the little metal piston is installed upside down, the tensioner won't work.

 

While it is making the noise at idle, bike on jiffy stand, take your boot or something and apply forward pressure to the outlets of each muffler. First one, then the other. The rubber hangar bushings can interact with the chrome straps that go through them. I change mine every year. The sound will follow up the pipe and you will swear the bottom end of your motor is falling apart.

 

Did you install a cover over the gear shift linkage...that will rattle?