Consider large cloud of gas. Assume it is electrically neutral (but as always, matter is composed of smaller things which are actually charged). Is it possible that propagation of sound waves in this cloud leads to emission of electromagnetic radiation?
My random thoughts about it:
I am not sure what mechanism could lead to that. Maybe some local oscilating dipole moment could appear? This is not completely unplausible - I could imagine gas molecules in some tiny volume element polarizing a liitle bit every now and then when density in the volume element goes up. But this would require the gas to be highly non-ideal.