Garbage disposal knocks loudly only when first turned on

Symptoms

• Loud knock or thump right when the switch is flipped on
• Noise settles down after the first second or two
• Runs smoothly for the rest of the cycle
• Happens fairly consistently every time

Likely causes

• CommonSmall debris resting against the flywheel at rest that clears once spinningA light piece of food waste can knock once before being flung clear.
• PossibleFlywheel starting from an off-center resting positionOn some units the flywheel can settle unevenly between uses.
• PossibleMotor mount or bearing play that's most noticeable at the torque of startupStartup torque is higher than running torque, which can highlight a bit of mechanical play.

What to do

1. Turn off and unplug the disposal.
2. Check the chamber with a flashlight for any resting debris near the flywheel.
3. Turn the flywheel through a full rotation by hand with the hex wrench, feeling for any catch or resistance point.
4. Clear any debris found and restore power.
5. Test a few more startups with water running and no food to see if the knock is consistent or debris-related.
6. If the knock continues every time with a confirmed clear chamber, it's likely mechanical wear rather than debris.

Tools and parts

• 1/4-inch hex wrench
• Flashlight

When to call a pro

If the startup knock is confirmed mechanical and not debris, a plumber can advise whether it's worth monitoring or replacing the unit.

Safety