HELP! Reoccurring spoiled milk problem

I've been getting a reoccurring problem for the past month. I leave a new carton of milk in the refrigerator, and it goes bad in about 5 days. This does not happen to every carton of milk, it happens to every second or third carton. But it does not happen to sealed jugs of chocolate milk.
I'm starting to suspect that the refrigerator is starting to die on me; does anybody know a healthy average temperature of a regenerator?
I also could be wrong. Does anybody know whets going on?....I'm also suspecting that bacteria is culturing in my refrigerator.
I'm starting to suspect that the refrigerator is starting to die on me; does anybody know a healthy average temperature of a regenerator?
I also could be wrong. Does anybody know whets going on?....I'm also suspecting that bacteria is culturing in my refrigerator.