During testing of a replaced aileron trim actuator we discovered a rumbling/vibrating flight spoiler #2.
The cause was play on one of the bearings located on the spoiler housing. This play was causing an output signal to the input lever of this spoiler actuator. Input and output signals are counteracting each other which results in this abnormal vibration of the flight spoiler. The solution to this is to replace the spoiler actuator or the bearings inside it. See picture.
Valid for 737 classicsd and NG !