I doubt it's timing chain related.

The clicking/knocking is probably engine ping you are hearing. If the get up and go is no longer there, it could be struggling to get exhaust gases out of the engine.

Or it could be a fuel related problem where it's pinging because it's lean.

For test I'd grab a temp gun and see just how hot the cat converter is getting. If it's plugged up bad, it would start glowing when it's really dark outside.