Hi,
my 1941 chevrolet coupe makes a very strange screaming/screeching noise.

When idling, the engine sounds fine and runs smooth. But when revving the engine in neutral, this strange noise is coming (I estimate at about 1000-1500rpm), at higher revs the noise disappears.

I took the belt off and ran the engine but the noise is still there, so water pump and generator are not the problem.

Does anybody have an idea what could be the problem?

The engine is a stock 216.

Here is a video of the noise:

Maybe a vacuum leak possibly. Double check the carb base plate to the main body and also the mounting bolts to the intake flange to intake. If they are tight, it could be cracked base gasket. You could try the carb cleaner in a spray can trick and spray around those areas with it running to see if it revs up when you spray it. If so, then that's where its sucking air....Good luck!

The engine sounds a bit dry to me. Like oil is not getting to the valvetrain. Has there been a recent oil change? Or maybe I am not hearing it right.