Banging Noise

If is sounds like a hollow metallic sound then the compressor is likely out of position os the unit has been mis-treated. if this is the case then the compressor will have to be changed (should be a 5 or 10 year wty)
If is i a light sounding tap then it is likely to be some of the copper tubing is hitting the chassis. There is a metal or plastic cover that runs along the back lower part of the fridge, remove this and gently rock the fridge to see if you can re-create the noise.