Whenever I strum pretty much any string, I will pretty much always have other strings ringer. The main suspect of this is the low E string, where most of the other strings ring. The ringing isn't very loud, but it is still annoying to the point where I wouldn't be able to play live without it being heard. Of course, I wouldn't play live with a Squire strat, but I still need help with it. Anyone know what it is?
i'm not too sure what it is but if you have a sister or you can nick one of your mum, get a hairband and stick just around the nut on the neck, not too tight though just have it resting and it will cut out unwanted vibration
It because the strings you are playing are vibrating, sending their resonance into the guitars body and form the body into the other strings. If you're playing chords then just mute the other strings with your left hand, if lead then mute them with your picking hand.
Gibson Firebird VII

pretty much spot on. if something on the guitar is vibrating, it'll send that energy throughout the rest of the guitar causing anything else thats not quite secure to vibrate as well.. strings mostly.

also, you can look up sympatheic vibration on google, and you'll see a neat experiment where if you take a 2 tuning forks and place them on either side of the room, hitting one of them to sounds its note will cause the other pitch fork to vibrate as well.
Grammar and spelling omitted as an exercise for the reader.
I'm not quite sure, but i think it's because the string is causing the same vibrations that the other loose string would do if you'd pick it. (ex. Picking 3rd fret on e string will cause g to vibrate). Not sure though
Its technique. Just something you gotta concentrate on correcting. The hair band or sock trick just covers up the issue not fixes it.