you will find this post:
Tick, tick fixed tnx to Donnie!
The end of these oil tubes blow out and cause the lifters to loose oil supply. Had this happen to me as your read from the above post.
Now the tubes are fixed and it appears to be a worn lifter that needs replacing but I don't know which one! So, since it's intermittant, I live with it for now.
This is NOT a common problem as far as I know.