Frequently when I am out walking the dog I see cloud formations like this.
It always makes me wonder: Why do clouds form these waves? And what is their resonant frequency? If you can see the waves from this far away, I guess the frequency is really very low. Probably well below what the human ear can detect, but maybe not below the range that elephants communicate in.
A little later. I just Googled the subject. Simple answer. And sure enough, the wind is blowing today and this is in the lee of the Franklin Mountains.