What evidence is there that we hear Ultra Sonic audio?

[Shannon]

There's nothing wrong with MP3 format itself as long as the proper care was taken in the files' preparation. Certainly it is safe. Worst possible case is that a particular file was down sampled into harmless static. Not impossible, mind you, but highly improbable.

I have found that mp3 default settings on a lot of compressors destroy ultrasonic audio or severely damage it. That's usually set for 128k.