Wow!

[timelets]

Angelo Esposito at Columbia University in New York and his colleagues calculated the relationship between sound and gravity, taking into account complicated particle interactions that had previously been ignored. They found that, although the effect is small, sound waves should have negative gravitational mass.

https://www.newscientist.com/article/2176191-sound-waves-are-a-form-of-antigravity-because-they-have-negative-mass/

The original paper is here https://arxiv.org/abs/1807.08771