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.
The most common cause of a clicking sound is neck muscle spasm, usually of the trapezius muscle of the back or sternocleidomastoid muscle of the neck. This spasm may be caused by : Poor posture. Hunching when walking or sitting and stooping over a desk for long periods of time.