1998 Saturn SL2 1.9 liter knock

I noticed a posting on the 1.9 liter knock. My car is doing the same thing. I wonder if it is in the timing chain. It seems to speed up and slow down when cranking the engine. Just before the battery dies, it will run only for a few seconds. It does sound like the knock is in the top end, and the exhaust at the same time. Do you know what causes this before I start teardown? The previous owner thinks it is a lifter. I know that would be hard since it is overhead cam! It has occurred to me, though, that it cuold be in a valve or cam follower in order to hear it in the exhaust. Please help, Joe