Some people are really slow to learn
and that includes me.
I had same issue. I have a chinese iphone copy whiich looks identical to the iphone in every way except it's android 2.3.3 It was going to silent mode by itself, or so I thought. When the the phone goes to sleep it is not in silent mode. Soon as you wake it up it is in silent mode. The reason for this is the top button above the volume buttons used for wake up has another function, it switches silent mode on or off depending what state it's in before you press it to wake up. So your phone is asleepand you wake it up by pressing the button...... you have just put it in silent mode without knowing. To fix the problem, if the vibrate indicator is showing on the toolbar press the wakeup button and it's sorted. So simple isn't it, but it foxed me for weeks. Also , now I don't use that button, I use the power button instead. A quick press wakes it up or puts it to bed and it does't affect the mode.:biggrin::biggrin::biggrin: