Via Author, lolikitsune tweets:

watched Mouretsu Space Pirates 3: noise in space. SEEMS LIKE THE SUCCESSOR TO STARSHIP OPERATORS IS NOT HERE YET

I like handwaving, so let me make an excuse for Pirates here. Actually, two of them. The first excuse is that a certain amount of noise might come through contact with the hull and thus with hull vibrations caused by the various machinery operating. But that's probably not good enough.

The second excuse is that everyone was in what we're told are very automated spacesuits, in an environment with fairly smart computers. People notice and react to sound cues. Thus, there is a good case for generating entirely artificial in-suit noises that correspond to important things going on in the outside world, things like airlock doors opening or potentially dangerous mechanisms in operation that you should steer clear of. So far all of the noises in space we've heard in Pirates have been noises from the ship itself, things that could plausibly be faked in the suits for this reason.

(By the way, I understand why shows love their sliding airlocks but I think it's a stupid design. As I picked up long ago from reading Heinlein juveniles, in theory the safest airlock door is one that opens inwards because then it's essentially impossible to accidentally open it until the inside has been depressurized. If the inside is still under pressure, you have many pounds per square inch holding the door very firmly closed. But inwards-opening doors would not make for good staging and good scenes, so we have the kind of sliding ones that we see in Pirates. This has been your digression of the day.)