You want to combine two expressions, loopOut and Wiggle. That way you can automate your animations but still get a more natural or random result.
I've got three different methods for you to try out. The first method uses a slider to manage the loopOut which is then added to a wiggle expression on the position (or any property). Then I show you Dan Ebberts' option for this which does not need a slider. Finally, I dig out a completely different take which allows you to repeat a wiggle precisely while looping.
