You can turn notifications on and off for each app under Settings > Notifications. Turn them all off at the top as an experiment to see if that stops the beeping.
If it is beeping (not the usual notification sound) at regular intervals (every so many seconds) it may be reporting a RAM problem; so I've heard. Try reseting it, and if the issue persists call Apple Tech Support.
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears.
Reset: Hold down the power and home buttons until the Apple logo appears. The iPad will reboot. This usually takes a bit longer than a restart.