These intermittent freezes are always caused by either the wrong Intel Rapid Storage Technology driver (automatically installed by Windows Update - it's incompatible with the system - YOU NEED TO DOWNLOAD THE CORRECT DRIVER FROM THE MANUFACTURER AND STOP WINDOWS FROM AUTOMATICALLY UPDATING DRIVERS - sometimes just installing the proper driver isn't enough. You have to do a nuke n' pave and then install the right driver), or a missing RAID or storage controller driver. Pull up the task manager and look to see if the disk usage goes up to 100% while it's freezing. If it is, then that's your problem.
I love this issue as it's bringing me in a lot of money from people that think they know what they're doing with computers and install their own SSD's. It brings 'em down a peg or two and makes them think twice about doing stuff themselves next time.