Some members have found that 'Settings', 'iPod', 'Sound Check' needs to be 'Off'. If that doesn't help, it might be worthwhile trying the universal 'fix all problems' cure, of completely turning the iPad off rather than simply putting it to sleep.
Does it affect all apps or just some? If it only affects a particular app, then try completely shutting down that app in the multi-task bar - double tap the Home button to open up the multi-task bar, press any icon until they start to jiggle then press the 'X' on the top left hand side of the app that's causing the problem; this will completely shut it down.
Now tap the Home button again to close the multi-task bar and then try the offending app another time.
Hope some of this works but, if not, get back to us.
Tim