High CPU usage due to USB 3.0 on Precison 4800

CPU usage is minimal until a device is plugged into the Precision 4600 USB 3.0 port, such as a printer.  Unplug it and CPU usage goes to 17% or better -- enough to occupy a couple of cores with interrupts and get the fan spun up to turbo-prop speed.  BIOS is the latest version (A25) and USB 3.0 drivers are the latest version (2.5.4.40) .  It hasn't always been this way -- possibly starting with the last BIOS update.  Current workaround is a reboot, or possibly hibernation.  Suggestions?