There is randomness there, but it'd require a lot of filtering to get: there's a lot of rhythms too. The lavarand stuff already mentioned probably resembles wha

There is randomness there, but it'd require a lot of filtering to get: there's a lot of rhythms too. The lavarand stuff already mentioned probably resembles what you'd need. Once you're going to all that work the noise source you use can be almost anything: sensitive enough ADC hooked up to a ground rod would probably do.