A really odd problem...solved! Now what?

Well this one took a little longer than it should have, and it's an odd one.

The problem started after i swapped on hydroboost. When the engine is warmed up, and when i was decelerating (e.g. coasting in gear down a hill) a horrible squeal would start up. The noise sounded exactly like a belt squeal. The noise seemed to come from everywhere. If i put the engine in neutral or revved it, it would go away.

My first thought was that i spilled something on the belt. New belt, no dice. Check the idler pullies. Nope. New tensioner? Nope. Okay...got a squeaky bearing in the alternator, so let's try that. Nope.

Eventually i did what i should have done to begin with, and took the belt off. The noise persisted. Well great, it must be something internal. Blew up my oil pump? Timing belt bolt backed off into the cover plate?

So here's what it ended up being:
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Not my video, but same problem

I believe that the cause of the problem is the new valve covers that i installed at the same time as the hydroboost (who'da thunk?).

I'm actually not sure what to do at this point. There is enough vacuum in the crankcase that you have to yank on the oil cap to get it out! Crankcase vacuum is a good thing, but this noise is wayyyy too irritating to leave alone. I could put one of those little clamp-on mini filters on the old PCV hose connection on the valve cover (I swapped to the late LS6 PCV setup).
Or is there a gasket that i need to replace? I seem to recall the bottom of the manifold being sealed by foam tape basically.

I have not been able to find discussion about this on LS1tech but maybe i'm just not searching for the right terms.

I figured it out.
Originally this motor had two PCV connections, one on each valve cover. When i switched to the newer PCV system i deleted both of those connections and just ran the one from the lifter valley cover to the throttle body.

I should have left one of the connectors from the valve cover to the upper connector on the throttle body. Problem solved!