Ours is frost free too , it was an ice blockage on the fan causing our problems.
Eat all your food from the freezer and bung the fridge stuff in the garden.
The source of the problem was caused by the fridge door being left slightly ajar at some point.
Our frost free hotpoint F/Freezer was making the same noises for 6 months or so before finally "giving up" completely before christmas.
After speaking to a mate in Milton Keynes who is a refrigeration engineer , we were advised to empty the fridge and freezer for 24 hours , leave the doors open...