(And with The Expanse having shown such signs from Episode 1, it almost seems like nobody can make a good sci-fi TV show that has spacecraft but not the supernatural.)
The Expanse isn't hard sci-fi, but it's a pretty decent sci-fi thriller in my opinion.
Given how the distortion sounds, the Fleet apparently uses single sideband (SSB) modulation for its radios. Amplitude modulation has a carrier and two sidebands; SSB suppresses the carrier and keeps only one of the sidebands (USB = upper side band, LSB = lower side band). That way, the transmitter uses bandwidth and power more efficiently. The downside is that it's harder to receive and there are some distortions. A good explanation of why there are those distortions: https://ham.stackexchange.com/a/392
Cool video showing SSB distortions: