This sounds JUST LIKE a intermittant ticking noise that I have been chasing. It sounded like valvetrain noise. But, I just realized that it has been my AC clutch. Try pulling your AC belt. Its a long shot but...

Did you pull the valve covers off and look again? you won't really see anything until you pull the rockers off. If it's a dead lifter you'll be able to see where the pushrod has been slapping the rocker. Start there and save some time. If you don't find the problem up top then obviously the motor needs to come apart!

Hmm.. Your issue sounds very similar to mine. I am not home so I can't tear into it so if you figure it out let us know.... Here is my vids.. Good Luck..

http://i123.photobucket.com/albums/o..._camaro002.jpg

http://i123.photobucket.com/albums/o..._camaro001.jpg

This is the same sound my car was making, it would increase with a rise in the RPM. I was on my way to the shop to diagnose it, and my car went boom. Blew a connecting rod through both sides of the motor, and down through the oil pan. Get that shit check asap!

Odd I have a tick that increases w/ rpms also but it only does it when the car has been driven awhile and then it seems to subside after awhile.