B737-400
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Returned To Gate; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Immediately after lift off; we experienced a continuous light shudder. Gear and flaps were retracted on scheduled. The unidentifiable shudder continued to increase as airspeed increased. No shudder was felt at the control column. We requested an immediate  return to ZZZ. Following an uneventful return to land; taxi in; and shutdown at the designated parking position; it was discovered that the aircraft had a detached elevator balance tab. During the previous flight; when flaps were partially extended; a similar shudder was felt. The shudder ceased when landing gear was extended; and flaps were extended to the 30 position. During a detailed post flight inspection of flaps and gear doors; nothing was detected. The shudder was first felt in the previous approach; when flaps where partially extended. It then disappeared when landing gear was extended; and final flaps were selected. As a result; the post flight inspection was heavily focused on those two main components; flaps and landing gear doors. The balance tab; although included in the post flight inspection; did not appear to be completely loose. A more detailed inspection of all secondary flight control surfaces may have exposed the potentially damaged balance tab.
Captain reported an air turn back due to aircraft shudder.