If your garbage disposal makes a rattling sound, you should turn off the power ASAP to avoid damage to the machine. The cause of the noise is probably a hard object, such as a bone, utensil or some other item, that fell in. There's also a chance a bearing is loose in the motor, but a garbage disposal bearing noise is easy to distinguish from the noise hard objects make as they get tossed around inside the canister.
The repair strategy is clear for an object in the canister that shouldn't be there: Remove it, but do it safely. If you turned off the power expeditiously, the damage should be minimal. A loose bearing in the motor is a bigger problem and may mean you need a new garbage disposal.
What's Making That Loud Noise?
Many people think a garbage disposal has blades and cuts up what you put in it, but it doesn't. The oval metal objects at the bottom of the canister are impellers, and their job is to fling food against the side of the canister, which is where the real shredding happens. The shredder ring, which is only about an inch or two wide, works on the principle of a cheese grater.
If you put a hard object in the disposal, it gets flung repeatedly against the shredder ring, and the noise can be horrendous, but it's misleading. The shredder ring isn't shredding, so it's relatively unaffected, and the impellers may get a dent or two, but they won't be permanently damaged either. Remove the object, and everything should return to normal.
Removing an Object in the Garbage Disposal
Never reach into a garbage disposal with your hand. If you need to retrieve a spoon or saltshaker, use a flashlight to locate the object and remove it with a pair of kitchen tongs or similar gripping implement. If the object broke up, retrieve every piece you see to avoid small pieces getting stuck in the gap between the rotor and the shredder ring.
When something hard, such as a bone, breaks up in the garbage disposal and small pieces get lodged in that gap, the rotor can't spin and an internal breaker shuts off the power. To restore operation, spin the rotor with a broom handle or use a hex wrench to spin it from underneath to dislodge the obstructions. Retrieve them, press the reset button and turn on the faucet, then run the disposal to clear the small pieces you couldn't retrieve.
Garbage Disposal Makes a Rattling Sound
When the garbage disposal makes a rattling sound, it could be due to a problem with the unit itself. When this is true, the noise isn't as jarring as when something falls into the canister, but it's more persistent.
One cause of such noises is that the garbage disposal impeller plate is loose. The impellers are supposed to be able to spin, but they aren't supposed to be able to move back and forth. When they can, it's because the screws holding them are loose. Unfortunately, you can't tighten them without disassembling the appliance, so it's time for a service call.
The rattling sounds could also be coming from the motor, and if so, the performance of the disposal will be affected and it will probably get stuck often. When the bearings are gone, you may be able to fix the motor, but it's probably cheaper and easier to buy a new garbage disposal.