Squeaking noise after warm up.

[68ChevelleSS]

I have a loud squeaking, almost like nails on a chalkboard after my 68 is warmed up. It only does it over about 20 mph while driving. I cannot hear it at highway or cruise speed. just annoys the heck out of me. It also does not get louder or quieter with rpm. Seems like you hear it most while slowing down. Not brakes. Also will sometimes do it once warmed up and just sitting idling in park. As soon as I put it in gear it stops. So far I've disconnected the belts thinking it might be a belt driven accessory. Still squeaks. lol. I thought it might be something rubbing once everything warmed up with the headers and exhaust but I still have at least 2 inch clearance all the way around them. I also pulled the speedo cable out and tried it. Still squeaking! I'm starting to think either a cracked flywheel (cracked between bolt holes) or some sort of vacuum leak. It runs perfect even while squeaking. Its very weird and driving me insane. Whats your thoughts and opinions? Very embarassing and annoying to drive such a nice car that squeaks horribly. I've heard flywheels that sound like a knocking noise when cracked but never nothing like this. Any info would be extremely helpful. Just some info on the car: 383 450hp golens crate engine/brand new TCI Street Fighter TH400. Engine has about 3500 miles on it. Trans maybe 500 miles. Thanks.