Whenever I start to play audio on my iPad using the built in speaker there is a brief popping sound from the speaker. Then after stoping the audio there is another quieter pop about 8 seconds after the audio stops. This doesn't happen with earphones, just with the built in speaker. And it happens every time. I think what is happening is the speaker goes to sleep after 8 seconds of not being used. And there is a popping sound when it starts up and also when it shuts down. Is this normal? I don't have this problem with my iPhone.