From what you describe I am almost certain it is the cam chain/cam chain tensioner. If the tensioner just needs to click one more notch down it's a very easy fix. If you need to replace the chain it's a bit more work. I did it this last spring and made a short video, you can hear whether your problem is the same as mine at the start of the vid.
https://www.youtube.com/watch?v=wUBJ76LJVts
there are some good, simple ways to get the tensioner to budge that require no tools. Let us know if you want to hear them
https://www.youtube.com/watch?v=wUBJ76LJVts
there are some good, simple ways to get the tensioner to budge that require no tools. Let us know if you want to hear them