B737 Captain reported uncommanded flight control roll oscillations during an approach. The Captain refused the release for the next flight.

Narrative

A large uncommanded roll of approximately 10-15 degrees was experienced on arrival in ZZZZ below 3000 FT; Autopilot OFF; auto throttle OFF; Flaps 10. Continuous smaller roll oscillations continued as the aircraft was configured to Gear Down; Flaps 40 and then subsequently continued until the runway surface. Approach conditions were steady state winds of 9 KTS; stable airspeed; and stable descent rate. Pilot flying stated roll oscillations felt mechanical in nature with corrective control input required at regular intervals. After landing; the flight crew was advised by the aft Flight Attendants of an unfamiliar noise from the aircraft that started about the same time as the uncommanded roll. Two other flight crew riding in the cabin also expressed concern about the aircraft roll oscillations. The aircraft specialist was conferred and Dispatch with Maintenance Control were consulted on possible checks to perform to isolate the cause of the uninduced and uncommanded roll oscillations. Aircraft specialist found no issues with flight control movement and surfaces; including the #3 slat that had been removed during maintenance in the prior weeks. Chief Pilot and Operations were consulted with crew concerns about not finding the cause of the uncommanded roll moment.The crew believed that it was a safety of flight matter to accept an undiagnosed aircraft control problem while transporting passengers. The Captain determined that it would not be prudent to continue to operate scheduled service. A three way conference was initiated with Dispatch and Maintenance Control and the aircraft discrepancy was logged by the flight crew.