I just noticed it today, but last night I short belted it because my smog pump froze up. So maybe that has somthing to do with it. Also I noticed a small power steering fluid leak, not sure where it's coming from. I don't think it's rod knock, but I'm not 100% sure.
Remove the belt and fire it up. See if the tick goes away when the belt is off. That will narrow it down. If it is still there then its something in the engine. Or the tube that runs to the smog pump hoses and pipes aren't plugged.
If you took the pump off you may be hearing an exhaust leak. One pipe runs to the exhaust and the other runs to the back of the heads ( into the thermactor passages )