I am sure the AudioBox is fine, but all systems and setups are electrically unique, so sussing out "ground loop hum/noise" can be part of any setup and can take some experimenting to eliminate.
1. Make sure power conditioners, power outlets are properly wired, polarized and also grounded.
2. Isolate power for devices .
3. Isolate power to speakers away from computer.
4. Isolate power to hub away from computer and or speakers.
5. Try using a powered USB hub, this may isolate the grounding of the AudioBox away from the computer.
You are also encouraged to submit a support ticket if none of the above helps.
Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new