A network technician is troubleshooting intermittent connectivity on a GigabitEthernet link between two switches. The 'show interfaces gigabitEthernet0/1' output shows a steadily increasing 'input errors' counter with a large 'CRC' count, but zero 'collisions' and zero 'late collisions'. The interface remains 'up/up' at 1000 Mbps full duplex on both ends. What is the MOST likely cause of these symptoms?