FleetRunner

I've been working on getting my old s-chassis project out of the back of my shop recently, and I've started running into a really annoying noise out of the front end of the engine. I've been chasing it for a little while now, and have figured out that it is definitely not the power steering pump, and all the other pulleys are nice and tight with no wobble or drag. I keep coming back to the front end of the engine right under the valve cover.

Today I removed the valve cover to look at the top end and make sure my CAS was installed correctly (it was at least a tooth off, but is in right now). There was a bit of polishing at the tip of the CAS shaft where it sits inside the head, so I did my best to clean anything out of there and applied some grease before putting the CAS back in.
What I'm talking about if it's unclear (photo cred FRSport.com)


After that, the engine ran like a top for a minute, but once it warmed up the noise came back. I can feel vibration through the CAS cap, and when I use a long screwdriver I can hear the noise pretty clearly at the base of the CAS. The noise is RPM-related, for sure. I'm just crossing my fingers it's not the cams, lol.
Video clip of the noise
SR20det CAS noise? - YouTube

Has anyone ever experienced this before? Am I stuck buying a new CAS or is there something else I'm missing?