could be your WP shaft that hold your fan is out of true and on it's way out.. inspect your shroud for signs of wear/impact/rubbing from fan.. check fan blades themselves..

could be your harmonic balancer is giving up the ghost.. the nylon bushings wear and you get a wobble.. I 'spect it could first be noticed on revs..

does it happen when you are sitting still revving or while your moving only? that knocks a good bit of the questionable areas out by itself..

 

Only moving.

 

Can the PCV cause a metalic buzzing sound..?

 

just something to look at my left passenger side pcv breather valve was making a buzzing popping noise at high rpms replaced and gone. sometimes the pcv breather isnt fully pushed in as well or the hose puts it off axis. I always start with cheap fixes

 

Check the little heat shields that are under the exhaust manifolds and see if they are touching the frame rails.

Visually inspect the pulleys for wobble while the engine is running.