Yep, there's something in the teeth below the level of the grind chamber.
Some cheap units don't have the hex key on the bottom of the unit, which means you'll need to use a piece of wood like a broom stick to try and get in and start rotating the grind plate.
The worst thing I found for jamming a disposal? Unpopped popcorn kernels. They're fine if the unit is running when you put them in, but if one slips in before the unit's running it will lock everything up nice and tight.