B737-900
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Situational Awareness; Confusion; Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; Flight Crew Diverted
Aircraft
On climb out through approximately 15;000 feet;the aircraft started to bounce/oscillate up and down.  This was not normal and was unsettling. The elevator had been inspected due to a prior occurrence of the same thing. The oscillations could not be felt in the control column.  We [advised ATC] and returned to ZZZ uneventfully.
B737 First Officer reported uncommanded elevator movement in flight.