The normal operating sounds of some of your household appliances is something you're probably so used to that it has become background noise. But sometimes your ears can alert you to a potential problem with an appliance, as in it sounds different to its normal operation. This can be the case with your freezer. Your freezer operates in periodic vapor compression cycles, and this is the sound of the freezer "running." Once the cycle has been completed, the device reverts back to a less audible state, which is a barely perceptible hum. When the cycle runs more frequently, perhaps even to a stage where it sounds continuous, you know that there can be a problem. The freezer is essentially struggling to maintain its temperature. Hopefully the issue is a minor one, and before you call a freezer repair specialist, there's something you can do yourself.
Defrosting
Defrosting the freezer is the first step. A buildup of ice can reduce your freezer's efficiency, meaning it has to work all that much harder to do its job.
Unplug it and open the doors.
Remove any detachable components (such as internal shelves) and locate the drainage hole in the base of the freezer (not all models have them).
Ensure that the hole is free of any obstructions (such as old food that might have accumulated there).
Place something absorbent under this hole at the base of the freezer. A sheet of newspaper or an old rag will do.
Simply leave the doors open and wait, periodically wiping excess water away as the ice melts.
You can speed up the process by placing bowls of warm water inside the freezer. This is handy if large chunks of ice are present.
Once all the ice has melted and been wiped away, replace any detachable components.
Cleaning the Condenser Coils
This defrosting is only the first step, and you will also need to clean your freezer's condenser coils. These coils help to remove heat, and their ability to do so can be sharply reduced when they become dirty or dusty. With assistance, slide the freezer out from the walls so that you can access its rear. Clean the coils with a vacuum cleaner, using the soft brush attachment. You can also dislodge large clumps of dust using a plastic-bristled brush. Take care not to scratch the coils. A damp cloth can be used to remove caked on dirt and dust, but exercise extreme caution so as not to drip water into the freezer's internal components. The cloth should be slightly damp, not dripping wet.
Move the freezer back to its original position and reconnect it. Hopefully its cycles will now be running at their usual frequency. If this is not the case, then there could be an issue with one of the freezer's internal components and a professional will need to diagnose and fix the problem.