I'm having a similar problem, but mine will stop tapping after the car warms up. I was thinking that my oil pressure was low, could that be the problem with my car also, the lifters or oil pump?
It could be that the oil doesn't make it into the lifters until it's warmed up and fluid enough to get into them.
2004 Grand Prix GTP Comp-G
Stock, featuring more KR than you can shake a stick at