We've all had a virus and been a bit exhausted. Came downstairs this morning and DH said "You must be feeling better as you cleared out the cupboard." I had no idea what he was talking about so he sent me into the kitchen to have a look. Someone went through our main food cupboard (tall so 5 shelves worth), chucked out all the out of date stuff and stacked the remainder neatly according to type. Plus they emptied and reloaded the dishwasher, although we all do that as it's pretty quick and easy.
It wasn't DH or me. It happened some time after DH and I went to bed (very early because we are still getting over the virus). We have a 15 and a 12 yr old, but frankly unless one of them has a guilty conscience about something I'm leaning more towards the house elf theory. 
15 yr old is at home today, but I went out before he was awake and he was in the shower when I came home so I'll have to wait to ask him.