Re: Sure it's not valve hydraulic tappets?
My hydraulic tappets clack like crazy upon startup especially when my oil is even slightly low. It goes away within 10 seconds. I use Lubromoly MOS2 oil additive and it really helps. John, your problem is certainly not the tappets. A good place to check though would be the VANOS system, as this can also make tapping noises and may do it more under stress than not. I'm not a mechanic, so this is just a suggestion. Oil to the VANOS system is critical, and the tube that carries oil to it can be faulty.
Sometimes I wonder if 20W50 oil is too heavy for high mileage engines. My car seems to like 15W40 or 10W40 better, as the tappets don't complain as much upon start up.