Hi @urban323 ,
Disconnect the power to the refrigerator and use an Ohmmeter to check that the freezer defrost heater element part #408A - case parts below the evaporator unit in the freezer compartment is OK and not open circuit.
If the heater element tests OK (not sure what the resistance should be but it should not be open circuit, maybe in the range 30 -200 Ohms perhaps)
The banging noise seems to indicate that the heater is OK as the noise may be the ice “falling off” the evaporator unit in chunks rather than dripping as it is melted, but still worth a check.
Also check that the drain hole in the drip pan below the evaporator unit is not blocked and also that the drain tube leading to the evaporator pan (#308A case parts) which is located under the compartments near the compressor unit is not blocked by pouring a measured amount of water (1 cup maybe) down the drain hole and making sure that it all gets to the pan
The refrigerator goes into its auto defrost cycle approx. once every 10 hours. During this time the compressor motor and the evaporator fans are turned off and the temperature in the freezer compartment is allowed to rise to near 32 deg F to melt the ice buildup on the evaporator unit and the defrost heater is turned on to speed up the process as you don’t want the food to even being to thaw.
The defrost meltwater flows down the drain tube to the evaporator pan under the compartments to evaporate, naturally. When the temperature in the freezer compartment rises to the preset temperature indicated by the defrost sensor, the control board turns off the heaters and restarts the compressor and the evaporator fan to drive the temps back down again to the set operating temperatures. The defrost cycle usually lasts about 15-20 minutes.
As the defrost cycles occurs usually twice a day there is really not that much ice build up so it seems that if you’re hearing loud clunks that either the heater is not operating as it should (also check the power to the heater if the element is OK) or the drain is blocked so that the meltwater can’t drain and refreezes again when the compressor is restarted at the end of the defrost cycle.
Update:
It could also be a faulty defrost sensor (part #401A case parts) which may be indicating the incorrect temperature thereby ending the defrost cycle prematurely which is not allowing a long enough time for the defrost cycle to melt all the ice, but try the above checks first