Front Valve Cover Sound?

[ptcfast2]

Alright, so I rebuilt my 98' Lumina's 3.1 top end (head gaskets, intake gaskets, sent out fuel injectors for cleaning - the whole deal) about a month ago. All has been good (no more fugly coolant! ) and I'm actually quite happy as it was my first top-end rebuild as a home mechanic....until now. It became a bit noisier than normal a few days ago, so I wiped out my stethoscope and had at it.

 

First off, it out my alternator is starting to make some really horrible noises (which explains the sudden increase in sound). I also noticed a slight "tapping" (tap your fingers on your desk rapidly to get an idea of the sound) that is emanating from the front valve cover. It does not happen until the car has warmed up. The rear valve cover area does not have this problem and has the standard humming noise you would expect to hear.

 

During the rebuild, I cleaned all the rocker arms/push-rods before I put them back in the engine and torqued accordingly. The tapping increases and decreases as the engine revs. As far as I know, it's not lifer related as the sound can only be heard very closely to the valve cover (and the engine used to have sticky lifters which are now fixed).

 

Any ideas as to the cause? Bad rocker arm or valve spring? I'd rather be prepared when I take off the valve cover. Keep in mind this engine has about 223,000 miles on it...