Phantom sound disappearance is a recurring issue for me. I have a difficult time touch typing on the iPad with no sound, the sound gives my brain that feedback "blackberry" feel. I have an iPad 2 with iOS 5.0.1. I keep my side switch set to "lock rotation" because I enable/disable my lock frequently. I find that often enough for it to be a nuissaince this problem reoccurs. I am the sole user if my device, no one is changing my settings. Each time this problem occurs, my solution is to go into Settings > General > change side switch to "mute" > toggle side switch to "sound on" > exit settings and confirm sound is on > return to settings and change side switch back to "lock rotation" > go into words with friends and have fun shaking my iPad to jiggle the letters and make that bloo-doop sound.