I was driving home today. Not pushing the car hard or anything and when I got home, I noticed a loud hiss. Thought it might of been the radiator or something, but when I popped the hood, it looked like the alternator was a mirage. There was alot of heat comming off of it.

What could this mean? It's a brand new alt.

Sounds like a potential fire to me, could be something shorting out inside the alt, check to see if any of the wires coming off of the alt are burnt, frayed or shorting out to ground, that could also be your problem. If you don't find any bad wires take the alt off and have it checked at a local parts store, they should find out if it is the actual alt that is bad. Either way it could start a fire if you keep driving it. Check that stuff out and let us know what you find.

I went back out to my car about 5-6 min after I got home, and it seemed as if the alt. wasn't hot anymore. And it wasn't hissing either...

Could it still be the alt? This is the first time that it has done this.

yes, it could be a bad alternator, if it was mine i would not even start the car until i had pulled it off & gotten it checked out.
it could be over charging which besides a fire, could burn up everything electrical that is turned on in the car.
pull the battery out & have it checked too as a bad battery could kill the alternator.
let who ever checks them out know that the alternator got very hot & was making a loud hissing nosie.
once you get it checked, let us know what was found.

Alright, I will take it in tomorrow.

Probably a bad bearing.........

mine was making that sound. Then it threw a bearing and frappe'd the internals.

Yup, went back to where I got it and had them test it out. Bearings were going going... gone! lol

Got my money back, went and got a new alt. from somewhere else. Not one of them remanufactored ones. All is well again.