1727, from Japanese samurai warrior, knight, originally the military retainer of the daimio, variant of saburai, nominal form of sabura(h)u to be in attendance, to serve..
The bubbles make a noise when they burst. This is called cavitation. Another cause for painless popping in the knee is when the ligaments and tendons catch as they go over a bony lump and pop when they snap back into place. Or the clicking and popping may be caused by catching on soft tissue or scar tissue within the knee.
1 Loose fragments of cartilage and other tissue can interfere with the smooth motion of joints. 2  The knee may lock or stick during movement. 3  It may creak, click, snap or make a grinding noise (crepitus). 4  Pain may cause a feeling of weakness or buckling in the knee.