Are you sick? Mostly likely its is from phlem in your lungs. Whenever I get respiratory infections (ie, bronchitis) I usually get a rattling in my chest and wheezing when I breathe. If you are sick this is most likely the cause and once you start feeling better it will begin to go away. If you aren't, I would suspect asthma.

Even if you do not feel sick, it could be pnemonia. There is such a thing as "walking pnemonia." this is where you do not feel sick, but your lungs fill up with fluid. Or it could be a sinus infection. Even if you do not feel sick your sinuses can be draining down your throat and into your lungs.