On the tape hiss issue: Different people have different abilities to hear very high-frequency sounds, especially since that ability tends to decline with age (presbycusis, as I mentioned earlier). So not everyone would be able to hear something as high as tape hiss. I'm actually a little surprised I don't seem to be losing any of my high-frequency hearing yet.
And the tape hiss only seems to be on the pilots and "The Man Trap." I didn't notice any on "The Naked Time." Also I'm not sure how much of it was hiss. There seemed to be some sort of ambient sounds from the recording studio or something as well.