2001 Impala Screech Noise at Idle

I have 2001 Chevy Impala with 3.8L engine that makes a loud screeching noise from the rear of the engine near the flywheel. The noise sound like two pieces or metal rubbing together.

The noise is not present when the car is first started and at idle. I rev up the engine in park and at about 1800 RPMs the screeching noise starts and can be heard. When returning to idle the noise remains.

Once the noise is heard, I continue to hear the noise when the RPMs reach 2500. The noise seems to get faster and slightly louder as RPMs increase. Above 2500 RPMs I can't hear the noise. That could be because the engine noise is louder.

When I turn off the car and restart, the screeching noise is not present. The engine needs to be revved up to 1800 RPMs for the noise to be heard again.

I removed the serpentine belt and the screeching noise is still present. So it is not a bad belt or accessory (PS Pump, Water Pump, Tensioner, Alternator, or AC Compressor)

I checked the PVC valve and it is not stuck.

I removed the Oil fill cap and the noise seems to go away most of the time.

The transmission was rebuilt yesterday. The noise was there before the transmission was rebuilt. The transmission mechanic examined the fly wheel and saw no signs of rubbing. The mechanic also checked rear main seal and that was fine. The New Transmission and torque converter were disconnected from Flywheel and engine started with not serpentine belt. Noise still present.

Any suggestion what is making the noise and how to repair it?

make sure the pvc o rings are both new.

I replaced the PVC Valve and both O-rings and the problem still exists.

I also notice that the noise is not present when engine is cool. Seems like the engine needs to be warmed up. Maybe the problem occurs when the system is running in open loop.

Any further ideas?

Something is not seated or wrong with the map or pcv o rings.