I doubt that reformatting a card will help this. I noticed that if you shoot a sequence and follow it with another sequence too soon, you will not hear the 'pretend' shutter sound especially if you're doing 5 frame bursts.. That is because the memory buffer is too small to hold the files that are queued up to go to the card. and there's no room left for new exposures to be stored in the buffer. I've noticed that even though the sound may be missing (a glitch with the app) images may still be written to the card. Look at the shutter button to the right of your screen after you make the exposures. If there is an animated rotating circle icon that means that the files are still being written. If you can wait for that to stop, then the sound will resume with the next burst and all will seem normal.