Ok, to be clear, is it a very very regular ticking or more of a hollow knocking?
If it's a ticking then it's likely to be a lifter, if it's a hollow knocking that's not always regular then yes chain slapping on to the guide at the top.
I had this when i'd installed all new timing gear and tensioner. I was gutted when it made the hollow knocking. Trouble is when you take the cam cover off (the big black bit
) you can't really see anything with it all static and it's no good just feeling the chain because the tensioner keeps it taught.
In my case, what was happening was that the ratchet on the new tensioner was being overcome when the chain was pulled tight, giving way and then the chain would go loose and slop and knock on the top slipper under the cam cover. As soon as the engine was stopped, there was little tension on the chain and the ratchet would pop out again making the chain taught. Caused me a bit of a puzzle that one but in the end I threw the new tensioner away and put my working old one back in and job done.