It is probably the fan in the freezer compartment not working correctly. This may be due to the fan starting to ice up. If the fan is not working correctly then the air is not getting circulated correctly. If you check you may find that the temperature in the freezer is above what it should be. If this is the case, switch off the appliance and allow to defrost for a good 48 hours. Even though it may be a frost free freezer. They in fact do ice up, especially around the fan. This is what happened to mine and it cost £120 for a new fan. Easy to fit just awkward getting in to do it.
Jim
November 2010