You may have cam chain stretch. You should take off the valve covers and rotate engine until you can see the cam timing marks and see if there is a 'stretched' difference from one cam to the other. On the other hand, if you know it has been a long while, or if you don't know when the chain was last replaced, just go ahead and roll in another one and put in a new chein. Not really a big deal and is peace of mind in the long run. It will get rid of that clatter on the first 2-3 seconds of start up. I just converted my single chain to a double chain in my garage at home. It cured the clatter and I have peace of mind.
Of course, I think you have the double chain already, you just need to roll one in.