Just stumbled onto this article explaining how it has been shown that sound, in a sense, can travel faster than the speed of light — Mach c. From the article:

For the first time, scientists have experimentally demonstrated that sound pulses can travel at velocities faster than the speed of light, c. William Robertson’s team from Middle Tennessee State University also showed that the group velocity of sound waves can become infinite, and even negative.

[...] the researchers achieved superluminal sound velocity by rephasing the spectral components of the sound pulses, which later recombine to form an identical-looking part of the pulse much further along within the pulse. So it’s not the actual sound waves that exceed c, but the waves’ “group velocity,” or the “length of the sample divided by the time taken for the peak of a pulse to traverse the sample.”

Perhaps it’s time to brush up on the physics, as at first glance I’m having a hard time understanding the article.