Pixalated and paused picture on recorded shows

Our Contour DVR recordings pixalate and the picture completely breaks up sometimes 2 minutes, sometimes 15 minutes into a recorded program.  This only happens on recordings, not regular programming.  It happens on different channels / programs / and times.  I've reset and rebooted many times without success.  I have proably 30 programs recorded (still with plenty of available space), so the last thing I want to do is to replace the unit and lose all of these recordings.