While I don't personally think that just using the word "noob" should get a person, I think that mods and muters should pay attention to disrespect a bit more.
"OMG you're such a noob lol" should not get the same response as
"You stupid Noob! You cant figure anything out! You noobs should all die in a fire!!!"
Basically if its said in a playful manner, its one thing, but flaming a person because they don't know something about the game, or the server should receive a mute.
I do agree with needing a longer mute time though!