XP2 and IS mode

I noticed that my 50-140 lens is always making some noise. It must be the IS system working. However, when turning off IS on the lens, it is still working. Also changing the IS mode setting in the menus doesn´t make any differense. When using my 100-400 lens it is opposite. I never feel or hear noise with any combination of the settings. Both lenses take sharp pictures. Have any in this forum similar experiences.
XP2 FW 1.01, 50-140 FW 1.11 and 100-400 FW 1.01