Engine noise
 

I'm having some problems with my car and any help would be appreciated as I have no idea whats going on.

The car is a 2001 m6 camaro with 80k miles. The last 4k miles or so the engine started making a noise that sounds like a marble or something rolling around the drivers side, it gets a little bit louder as the rpms go up but then I cant really hear it above 3500 rpm. Also its almost unnoticeable at idle.

When the car is in gear it will also sometimes make a tapping noise while I'm driving. If its in neutral and i rev the engine up it wont make that noise.

Again I have no idea whats making these noises. Thanks

Usually the sound of rolling marbles is rod knock. Can you take a video of the sound?

piston slap when cold?

...
 

its definitely not piston slap.

My iphone's camera sucks at taking videos so i looked on youtube and found a video of the knock that sounds real similar.

http://www.youtube.com/watch?v=nZhGCUP1h7g

I also read that it might be a loose rocker or lifter but whatever it is, it sounds a lot like the knock in that video.