Originally posted by Jasvox It's the sensor shifting...they all do it in the K10D. No problem to be concerned about.
Fortunately they've finally included a reference to it in the K20D manual:
"Shake Reduction (SR)
Shake Reduction (SR) on the K20D features a PENTAX original system which uses magnetic force to move the image sensor at high speeds, compensating camera shake.
The camera may generate some operating noise when it is shaken, such as when changing the composition of a picture. It is not a malfunction."