valve tappet or piston slap noise?

I have a 97 suburb (60,000 miles on this engine) with the 5.7l vortec. When it starts up cold in the morning(approx. 20F.) I hear a very load tapping
sound ... load enough to hear it a block away.. it sounds like hitting the block with a hammer at about 10 times per second. After the motor runs for a couple of minutes it goes away. I don't have to wait for the engine to warm up. It doesn't come back again until the next day. I suspect that it is a defective lifter but can't pinpoint where the noise is coming from.......sounds like from the center of the engine. Can't seem to pin point it to one side or the other. Another suspicious fact that could have something to do with the noise is......every day when I start up in the morning the check engine light comes on and when I check the code it states "misfire on cylinder #4". I also know that the spark plug on #4 fouls (hard white substance) and needs to be cleaned every couple of thousand miles. Plugs , wires, distributor cap, have been replaced. Could be wrong but am suspecting that the misfire is a bad fuel injector. A couple of quarts of oil also disappears every 3K or so. It sounds like all of the problems are at cylinder #4 but am afraid that I am going to have to go so far as to remove the head to know for sure. Really don't want to get into that until the weather warms up. Any thoughts appreciated.
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