external speakers keep cutting out

Using Harman Kardon sound stick USB speakers on my mac book and they keep cutting out after about 1:08 of use. It happens with all audio sources (itunes, online streaming etc.) and works immediately if I unplug and re-insert into the USB port.

On the sound settings, the "USB Sticks" stays highlighted as the source. The internal speakers do not come on when the sound stick speakers cut out, but do so when I unplug them from the USB port.

This problem just started out of the blue after years of flawless use, no software updates. Happens on both of my USB ports. Tried re-starting, didn't help.

So frustrated.