We have an imac 27 inch late 2012 system using a seagate 3 TB thunderbolt drive (stca3000101). We upgraded OS from 10.8.4 to 10.8.5 and this is when the issue started to happen. When the thunderbolt drive is plugged in the system will freeze. It happens sometimes right away or takes 5 to 10 minutes to freeze. We upgraded to Mavericks and the issue remains. Any suggestions?