LG Fridge making intermittent sound - like...

Question

LG Fridge just 1 1/2 years old. Just recently there is a noise coming from the back of the fridge that sounds like something is hitting a fan. Similar to the sound that a hockey cards makes when kids put it on their bike so that the spokes hit it. The noise stops as soon as you open one of the doors (split doors). The noise seems to be intermitent - not happening all the time. The fridge is 22cu bottom mount freezer.