The very first radiation to escape after the Big Bang has been traveling outward for 13.8 billion years. This cosmic microwave background has been literally stretched over time, it's frequency and temperature lowering as the universe, and everything in it, expands.
John G. Cramer from the University of Washington took the measurement data of the cosmic microwave background from ESA's Planck space telescope and converted the energy frequencies of the first 760,000 years of the universe into audible sound. He had to multiply it by 10^26 so we could hear it!
More of Cramer's mixes: http://dft.ba/-bigbangsounds