Since the Alpha 10 release, zombies are attracted by certain kinds of activity, that ‘heat’ up a place, and if they can’t walk or climb to the center of that ‘heat’, they’ll dig to it. The ‘hotter’ the spot (the more heat producing activity) the more they are attracted to it. If the zombies have a choice between heat centers, they’ll go to the hotter one.
Activities that (probably) heat up a place – zombies dying, campfires, mining, forges(?), cutting trees, dropping a sleeping bag, even farms might (before the latest update, I found a zombie standing in the center of my wasteland cornfield). Some activities seem to generate more heat than others, and the faster a particular activity is done, the more heat it seems to generate. I expect building would too, but not sure to what degree.
Eating, drinking, using boxes, walking upright – those don’t seem to generate heat. They’ll generate noise that the zombie hordes might pick up on, but during the day it’s not a big deal.