oil level is a couple of mm over the full marker on the trans dipstick. I've only heard the hiss while driving, but i thought it was corresponding to the revs it was doing, not the gear change...
I've never had it stationary revvin it's tits off before, but i've put the boot into a bit while stopped and couldnt get the noise, although i thought it was because of not revving it high enough to require the same volume of air as when i revved the crap out of it going along and it hissed.
My tranny is generally smooth as silk, yet tight, so i didnt think it would be that. Trans fluid is clean, and i've never given the auto a hard time coz i've heard they're pretty weak.