Linux Mint Forums

Welcome to Mint
It would have helped if you told us which Mint you have
You have to go through all settings for sound - not only in "Sound" in the control center but also in the mixer(s) - right click the speaker at the clock and open the mixer
Go through it and look for anything connected with USB

That's odd - have to think about it for a while and come back to you

I have never set up usb speakers in Linux but every thread I have found has been similar to this one.

http://ubuntuforums.org/showthread.php? ... gitech+z10

It is an older thread but the most complete information I could find on the subject.