1968 Dart sudden rear end noise.

Jack it up and pull the drums. You might get lucky and there's a spring in the drum that bounced around in there and locked the drum? You gotta start somewhere.
I'll have to do it tomorrow had to go to work. I'm hoping you're right. I had a brake return spring break on a 70 dart once but it just made the shoe drag and I never had this issue. It's making a gear sounding noise. Push the brakes and it goes away but then comes back in a few seconds even if you're still braking. When driving it would be grumbling and then make a sound like a marble bounching around and the make a pop or bang like it was getting caught in something. I ordered some springs just in case. Nobody had them in stock