Also seen this and haven't worked out what it means yet ... would be interested to know?

Glurin wrote: »

The only theory I have is that something or someone is fighting nearby, but there's been a handful of instances where I finish the dig almost at the moment it happens and there's nothing around me.

I think the game thinks you want to rotate the dig window?

I also think it's fighting near you. It happens alot in Rivenspire near the west most anchor. I don't know if it's a quest or a grind spot, but a lot of players going in and out of a nearby tower, with enemies spawning nearby. Most dig mounds are away from mob spawn points, (helpful if you're running around looking the mound, can probably ignore aggro range areas).

So my guess, even though your dig site my be out of aggro range it might still be within kite range, is that it serves as a warning that you might get pulled into a fight.

One final observation, I've had my screen rock after I've dug everything up, so most likely not related to actions done while digging.