Small rumbling (6)
I believe the answer is:
tremor
(Other definitions for tremor that I've seen before include "Quivering" , "Quavering" , "Small earthquake" , "Vibration - shaking" , "Strong shake" .)
I believe the answer is:
tremor
(Other definitions for tremor that I've seen before include "Quivering" , "Quavering" , "Small earthquake" , "Vibration - shaking" , "Strong shake" .)