Donuel: "highly ionized air prevents seeing many ufos in a hovering stationary position. The craft use vast amounts of electricity. They do make low frequency sound but self canceling waves may prevent it from being heard at a distance."

Possibly electromagnetic energy as well...and/or have you considered inter-dimensional crafts?....that is, if they are really as purported to being.

I have a musician friend who claims to have been abducted, and he is dead serious...I've made no judgment in regards to his claims...Though I do have some interesting history, crossing paths, but very circumstantial.

GfS