Thank you for a highly original and interesting post.
In 2628 where I am from, we have also discovered sounds emanating from alternate dimensions in sub space. Whilst even we don't fully understand where they come from, we do know that they are real and show signs of intelligence. They are mostly natural occurrences from beings in other dimensions rather than an attempt at communication with us.
We understand sound as a waveform that you hear with your ears here on Earth, but in outer space we can hear with other senses and therefore cosmic 'sounds' can and do move through the vacuum of space.