I have had the same exact problem before I got my new iPad.
First try double clicking the home button to bring up the multi-tasking bar. Hold an app that appears in the multi-tasking bar and it will start to jiggle. Press all the little "minus'" to delete them and stop them from running. When you close an app, no matter what app it is, it will be running in background. So it is good to do this once in a while.
If the problem persists restore your iPad. When your iPad is fully restored it will ask you if you want to use an old iPad back up. Pick "set up as new iPad" because if the problem was on the iPad, it will surly be on the backup.
And if the problem still persists go to your local Apple store. Make sure to set up a Genius Bar Appointment because usually they will not have any open spots. Explain your problem and they most likely replace it for you. If they ask to see the problem them-selves, meaning see it frozen, try going on a website with a lot going on like ESPN.
I hope you resolve your problem.
Regards,
Ralphy