Valve tick?

My '03 Gt with 27,000 on it is making what sounds like intermittent valve ticking. Starts about 30 seconds to one minute after car has been started and can be heard on and off until the car is at full operating temp. I already checked the torque on all my plugs and they're all >13 ft/lbs. Changed the oil and it still happens. It appears to be coming from the drivers side head near the intake.
Anybody have any ideas what this might be?
I already did a search and the only thing that came up was the spark plug blow-out situation which I already looked into.
All input is appreciated.

thanks for the replies.
I did the search for the "death rattle" and that sounds very similar to what I'm observing. Is there any thing thing that I should look into anyway? I already checked the exhaust, especially the manifolds, and its not a leak. The car isn't throwing any codes and the motor is bone stock.
Thanks again for your input.