Most amps will produce some hiss when turned on. For the type of music I described, with a functioning/properly designed amp, this shouldn't be loud enough to
require a noise gate. I've played plenty of amps 'really turned up'. When they're that loud, you usually can't hear the hiss over the ringing in your ears between songs.
Tuning doesn't make a difference at all regarding need for a gate - you're misreading me there. I was referring to the (typically) down-tuned styles of metal . . . this music is played with gain levels high enough that there's little dynamic range and noise is compressed/amplified to much higher than normal levels. The ability to switch between fully on (any sound from the guitar) and fully off (all strings muted) is very important for the percussive aspects of this music, so maybe a gate makes more sense there. It sounds to me like this is the style of music that you play.