Disposer noise comes from two sources.
1. Something metal is stuck in the teeth of the disposer and makes noise as the grinding plate rotates. Use good lighting and a long screwdriver and long needle nose pliers to fish around, find the object and lift it out. A long magnet can be helpful. If the unit spins, you may try grinding up the debris. But be cafeful and cover the opening; the object may fly out. It may make a lot of noise!
2. If nothing is discovered, the disposer itself is failing and needs replacement. Either the teeth or the grinding plate may be loose or damaged.
Normal Grinding Plate with Tooth
Broken Grinding Tooth