I finally got all of my cooling issues under control and the car's been running like a dream until this morning. On my way to work I heard a ticking sound coming from the engine. It lasted about 30 seconds and there was no loss of power, change in oil pressure, change in manifold vacuum, coolant temperature, etc. I thought that was strange but everything felt fine so I continued on my drive to work. Right as I was pulling in to the parking lot the ticking started again so I parked it quickly and popped the hood to see what was going on. Everything looked ok and the noise was obviously coming from under the valve cover, maybe the number 4 or 6 cylinder. I've heard this noise only once before, during start up after an oil change. Sure sounded like there was some lash in the valve train and the rocker arm was slapping around.
I understand that lifters can make this noise at startup if they bleed-down, but if that's the problem that I'm having, what might have caused it to start randomly doing this when the engine was fully warmed up and driving down the road?
Any thoughts, opinions, experiences?
Thanks