With the drive disconnected, reboot windows cleanly and see if the sound is better.
I need you to reboot windows cleanly. To do that please go to the run command and type in msconfig . Once that starts, select selective startup, and then uncheck the load startup items. Now click on the services tab, and down near the bottom of the window, check the box that says Hide all Microsoft Services now go up and uncheck all the services still listed, make sure you scroll down the list if need to unselect all the non Microsoft services. Now click apply, then click OK and reboot the computer.
Test the sound. Once you have decided, run msconfig and select normal startup then click apply then OK and reboot the computer and then let me know.