Ensure that you have installed the current device drivers.
Turn the Mixer Dial all the way to the left. You will hear only input audio. Noise ?
Turn the Mixer Dial all the way to the right. You will hear only computer playback audio. Test playback with iTunes and or YouTube. Noise ?
You might also test your AudioBox on another computer so to determine if it will have the same issues or not.
Every computer is different tho. Contact PreSonus Support for further assistance.