Hi Kevin
I've been through a lot of this in the past year, you can read about it here if you want to:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/826025-clackety-clackety-clackety-clack.html
I finally took my SC to an experienced P mechanic and he's fairly certain that what I'm hearing are the valves smacking closed into their seats. I already knew that the PO cheaped out and didn't rebuild the heads on the engine overhaul, so it is what it is.
My mechanic basically said that so long as we're sure that the valves are adjusted correctly then the noises are as described and aren't an immediate problem, but will likely worsen over time. So I'll drive the car this summer and then decide what to do next when winter comes. Good luck!