Diagnosis
Debris intrusion into the drive shaft seal. Hair, toothpaste, and minerals can jam the mechanism where the brush head attaches.
How to Fix It
1. Remove the brush head. 2. Inspect the metal drive shaft for visible hair or gunk. Use tweezers to remove any debris. 3. Soak a cotton swab in white vinegar and scrub around the base of the shaft to dissolve mineral deposits. 4. Dry thoroughly with a paper towel. 5. Reattach a brush head and test.
If That Didn't Work
The internal motor coupling may be worn. Try a brand new, official Colgate Hum brush head. If the noise continues with a new head, the internal motor assembly is failing.
Heads Up
Always rinse the brush head attachment area after each use. Never store a travel cap on the handle while it's wet, as this traps moisture and promotes debris accumulation.