Runs Aborting

I have a 5415C that initiates a run OK. But within a few seconds, the run aborts and the green pilot light starts to flash rapidly. Once the rotor stops the lid won't open. Have to power off, then on to get the lid to open. I also noticed the centrifuge hums when the power is on, but idle. I haven't used this model for many years and don't remember if there is any background motor noise when idle. I seem to think not. Thanks for any insight!

Equipment: EPPENDORF - 5415C