Don't forget about the EQ!
A guitar track that has a little bit of speakerhiss on it might be a big deal, but if you decided to make the guitar sound a little brighter by adding high frequencies, you've made the hiss much more audible. So not only the track and the channel have noise, but the eq settings can add a lot. So mute those suckers!
(now why am I too lazy to do it myself most of the times?)