I have heard of people who have this problem because of a faulty compressor relay - they can just go bad after a few years. Another possibility is that you put in a refrigerator bulb with too high-wattage: this can melt the plastic near the bulb itself.
It could be multiple things one of the things it could be are some refrigerstors have condensing units on them and yours may be plugged with dust or animal hair pull the panel off the bottom see if its plugged pull the back from the fridge so you can see it the compressor and fans are full of dust .