Put the car on ramps today and poked around the engine. When the engine is cold, there is no tick. Either in gear or out of gear. As the engine warms up, the tick shows up around the rear of the engine on the driver's side while it's in gear. If I put my listening device (long screwdriver) to the head/block/valve cover area, I can hear a slight tick. I't definetely more noticable outside the car. I'm thinking it could be a sticky lifter. I'm going to run a pint of ATF through it for 50 miles or so of easy driving and see if I get the noise to quiet down. Before I do that though, I'm going to pull the valve covers again and see if there's anything obviously wrong.