The universe is musical. Strange as it may seem, human beings don't have a monopoly on creating complex melodies. Birds are an obvious example, but everything from subatomic particles, rivers to black holes create tonal notes. Here's a violin playing a duet with some radioactive particles!
As you would imagine, many natural melodies sound rather strange. A collection of sounds from space, including sounds generated in the Earth's magnetosphere and the eerily creepy bloops from Saturn's natural radio signals, can be found here.
On the more recognisable end of the spectrum, beluga whales have been found to 'sing' in a way that has been described as 'human like'.
In a non-auditory sense, many natural structures share their patterns with music: a classic example being spider webs.
There is an increasing body of evidence that suggests that the tonal structure of music reflects more abstract and pervasive natural patterns: for example, the Fibonacci sequence and phi, the 'Golden Ratio'. A quick example of this is as follows:
The first few numbers of the Fibonacci sequence are:
1, 1, 2, 3, 5, 8, 13
Now, consider the following:
The ramifications of this are incredibly profound. The Fibonacci sequence and its resulting Golden Ratio is everywhere in nature: in the shapes of galaxies, whirlpools, sunflowers, the human body, the human face, the branching of trees, the breeding of rabbits and in honeybee linages.
Of course, musical structure wasn't 'designed' with this in mind: it implies that our human music mirrors a deeper, more integral melody that flows throughout the entirety of existence.
Things get even more mind-blowing when one considers a recent theory in particle physics. The so-called 'String' theory (or M-Theory to give it it's proper name), in the most fundamental of layman's terms, purports that the only difference between the basic particles that make up all matter in the universe is that they are essentially just different 'notes' played on infinitesimally small 'strings'. A more in-depth layman's explanation can be found here.
Literature connecting 'real' music with this subatomic music touches on the arcane, but is extant nonetheless.
Modern science is only now beginning to probe the basic fabric of the universe, but it seems likely that when we do fully elucidate it, it'll be melodious.
I leave you with something quite interesting: the number pi in musical form.