I installed a PCI USB 3.0 card and now one out of four cpu's keeps up running nusb3mon.exe. Meaning that I have a CPU load of 25% all the time. Did anyone have the same problem before?
http://www.delock.de/produkte/F_319_USB-3-0_89315/treiber.html?setLanguage=en

Had no problems with the onboard USB 3.0 ports of my Asus M4A89GDT. Operating system Window7 64bit