I once capped off the large left side engine breather hose on both ends.
( my thinking was that it was dumping oil fumes into the throttle body / intake manifold, but Rob at NeedsWings set me straight on this. )
Anyway, the end result was that after several days ( as a matter of fact, on the trip to the Dragon last spring ), I could have sworn the water pump was going out, the screeching was just as you describe.
It was sucking air into the intake around the poorly sealed opening.
You may have a split or something like that in one or more of the engine breather hoses.
Worth checking anyway.