Screeching

I doubt it has anything to do with the oil slinger. The oil pump drive is helical cut and this applies constant thrust on the cam. So unless the slinger itself is loose, it would be a constant noise. The crank is constantly thrusting forward from the pressure plate of the transmission. And it happens clutch in/out.

It is also strange that it happens at 2 different rpms. I would bet it is harmonics in this case, and that the tones are slightly different. A permanent solution if it's the exhaust is to use header wrap and band clamps.

A galled roller lifter bearing is plausible but I wouldn't think that it would last too long.

Are you able to vent the exhaust out the garage and close the door to make it quieter?