For the second time my 550D has kept losing sound for several minutes and coming back, the fault does not lie with the mic as its never happened using it on my HDV cam and i also always make sure the plug is pushed fully in the socket, as far as i can tell when it goes its at the start of a new clip and may have no sound for many clips,and when it returns its at the start of a new clip.If only they had audio level indicators like NORMAL cams.