Definitle a good idea just to pull the valve cover and inspect the timing chain and related parts.  I had a ticking sound from mince a while back, only at idle.  It took me forever to figure it out.  It sounded like the number four valves, or the egr, or the valve contacting the valve cover.  all that.  changed oil and filter.  I couldn't get rid of it.  Long story short, silicone gasket instead of paper on the timing cover got into the galley for the tensoiner, and made it stick, causing the chain to have slack.  That noise traveled down the block and sounded like a valve on the number four cylinder.  Anyway, check out the timing components, good luck