Feist's acoustic MM experiment is interesting but doesn't challenge the light polarization argument. He measured sound's two-way speed on a moving car and got a null result — which makes sense because sound waves entrain with the air medium moving with the car, just like light's speed is frame-independent in relativity.

The key difference: sound is longitudinal and has no polarization, which is exactly what you'd expect. Light is transverse and does polarize, which we measure constantly. If light were longitudinal like sound, we'd lose polarization entirely — but we don't.

Feist's experiment shows acoustic waves behave consistently with their medium, but doesn't imply light must be longitudinal. The vixra analysis notes the null result aligns with conventional wave theory in moving frames.