Is it possible some releases had re-equalization. Or some sort of digital clean up was done on the audio.
Often they get overzealous when trying to clean up an old monaural optical track from its clicks, pops or hiss and they ruin the track by using too harsh of a setting. Some people prefer no equalization or clean up be done.
Usually i prefer the audio remain untouched. But the depends on how bad the pops and clicks or audio hiss is. If it makes the film horrible sounding then some clean up has to be done.
Only really old films seems to have an odd pop and hiss like bacon, or an old scratched LP record playing.
Terminator is not that old. Why the New mixes i don't really know. Cameron probably is why.