constant activity if ethernet cable isn't plugged in

I’ve noticed if I start my computer without the cat5 cable plugged in,
then the computer’s activity light stays completely on,
and this starts before I log into a desktop.

This seems to be consistently reproducible.

What “activity light” do you mean? Check with “top” to see what the machine thinks it is doing. Do you have something running at start-up that is trying to access another machine , e.g. on-line update, or ntp daemon?

I just did a zypper dup, and it seems to have been fixed.

I think this is the weekly cron job.
I see it every monday when I turn the computer on.
If I leave and come back 5-10 minutes later the light is off.