Mac external speakers delayed when hitting volume button.

So once in a while, my external computer speakers glitches out and freeze when I try to adjust the volume on my Mac Pro. When I press the volume up and down buttons it doesn't respond for several minutes. Then when it does remembers every time I pressed the volume button and my speakers either go super loud or super quiet. Also once in a while, my speaker completely loses it, when I try to adjust the volume it gets delayed again, and then when it does finally adust it has a major glitch and freezes the speaker playing the last sound over and over again like a really bad echo. I need to run to the back of my computer and disconnect the USB wire from the speaker and reconnect it to stop the load from echoing. Does anyone know why this is happening and how to fix this problem? I am currently using Edifier G2000 speakers.