Samsung RS2556BB Refrigerator top half of freezer is not freezing?

I have a side by side samsung RS2556BB refrigerator. The top part of the freezer is not freezing but the bottom half of the freezer is working fine. The refrigerator side is cooling well also. It is also making a humming sound which has been loud at times but is not so loud currently. The humming sound also stops when I open the freezer or refrigerator door. I would greatly appreciate any help anyone could offer since it is difficult to find a technician in my area that repairs samsung refrigerators.