"For one thing, what if their music is in frequency bands down around 10 cycles per hour? And all their folk songs are at least a day long?"

Then all my recorded songs will sound like Alvin the Chipmunk to them.

Seriously, if they know we're here, they have to have senses that operate in at least some of our frequencies. Heck, rocks might be intelligent, but we'll never know because their time scale is so much greater than ours. Likewise with any critters we meet from "out there."

(Didja hear about the giant intelligent statue that was found on a planet around a distant star? All instruments recording both life and intelligence, but no one could figure out how to check either as the statue -- which was made of rock -- didn't respond to any stimuli. Finally, in exasperation, a scientist standing in front of the statue exclaimed, "WHY would the Almighty Intelligence that conceived the Universe create an intelligent, living creature such as this and then have it respond to no stimuli at all?"

No one had ever ask a question near the statue before, and it stood, drawing itself up to its full magnificent height, paused, and in a deep voice said, "It wouldn't." And sat down again.

The scientist slapped his forehead and shouted, "OF COURSE! OF COURSE! It only stands to reason!")