This is a very bizarre problem that I can't find in any other thread.
Yesterday, my iPad's audio output was working normally, but the first time I used it today the sound was distorted and reminded me of a badly tuned radio. (In fact every now and then I hear what sounds like classical music.) At first I thought it might be a problem with my headphones, which are decrepit anyways, but the distortion is also there when I use the built-in speaker. The hissing is loudest when the audio is just silence. I hope this isn't some kind of capricious bug.
Thanks for any help! This issue makes Pimsleur's Mandarin Chinese quite difficult to follow!
Reset the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider if it appears on the screen - let go of the buttons. Let the iPad start up.