If you hear the ticking in the head, it is running the ‘hunt’ action (the first part of the homing cycle). During this action, it acquires an ‘update lock’ which prevents the firmware updater from performing an upgrade.
The hunt cycle homes the focus, delivering those ticks in a total of 6 groups (tick-tick-tick, pause, tick-tick-tick, pause, etc… six times). and runs about 10 seconds.
If it reboots while that ticking is going on in the head, there is something else wrong. It is not likely a firmware update happening.
If it happened after it completed, its possible that the updater took over after the hunt action released the lock, but before the next step in the homing sequence started.