I had a similar problem with an aluminum Silverstone case. Turned out there was a grounding washer connected by wire to the front panel that had to be attached

I had a similar problem with an aluminum Silverstone case. Turned out there was a grounding washer connected by wire to the front panel that had to be attached to a screw on the motherboard (I think). Fixed USB disconnecting issues right up. (See: https://superuser.com/questions/64098/static-when-metal-usb-plug-touches-my-case-and-other-electrical-problems https://superuser.com/questions/64098/static-when-metal-usb-...)