It is making a clicking popping noise above the refrigerator behind the grate. It also sounds a bit like it is struggling but at this time the refrig and freezer are staying cool. Also I could describe it as rattling sometimes. The subzero is 21 years old

Question edited for clarity.

It sounds like the compressor is struggling / overheating / failing. When was the last time your stripped the back out and removed all the fluff and debris? It overworks the compressor and gets red hot when the condenser coils get blocked. The struggling compressor causes the humming. Turn it off, keep the doors closed and vacuum it all out. Clean underneath and you might as well clean the floor and walls around it as the plan is to leave it disconnected for 1 to 2 hours to cool down and settle the refrigerant gas/liquid. Some other ideas below.

The evaporator fan motor circulates air over the coils to help keep things cool inside your fridge. If this motor starts to go bad, it will make a buzzing sound as it struggles to circulate air. You'll need to replace the evaporator fan motor to fix this problem.
Aug 22, 2022

Frigidaire Refrigerator Runs Loud? This May Be Why...

Is this a clicking or a knock/pop sound? The knock knock sound can sometimes be helped a little bit by tilting the refrigerant filter drier (located in the compressor compartment) to a horizontal position. Ask your technician to do this for you.

Does not sound good. We need to find ou where the popping noise came from first. Not cooling is because it sounds like the popping noise is from that area but for sure that area. It could be a failed control board and shorted out the compressor relay.would like to go and do this yourself of have a technician like myself lead you through this? I'm going to get the service manual and if you would like a copy I will get it for you, Thanks and let me know soon, Sea Breeze
spotted cow make sure the model number above you post is correct before we begin

it might have a leak with the refrigerant and the compressor motor is having a hard time. Time to have it checked by a qualified tech if it's worth it

Frigidaire's make a popping sound when they first start up. It is gas bubbles popping out of the capillary tube into the larger evaporator. The fix for this is to have your technician call frigidaire and ask them how much nitrogen they need to add to your sealed system to eliminate the popping. Please note this sound will stop after about a minute so this is the key to identifying whether or not this is what you are hearing.

if you hear a clicking like the compressor is trying to start, like a clicking on and off this sounds like it could be your start run relay trying to kick your compressor on. if this is bad it will continue to click, and your compressor won't start. unless your mechanically inclined this might be the time to call a service tech. the start run relay switch sits on the compressor behind the fridge.

Water dispenser is a simple touch switch in door energizing a solenoid water valve behind ventilation grate above refrigerator. Water tube runs down into and ends at ice dispenser chute. Should hear solenoid click at top of fridge when activate water touch switch. Can unhook discharge side of solenoid valve temporarily to prove water output. If water dispenser tube acts blocked it could be frozen where it ends-look up the hole at the bottom of refrigerator control buttons.
Ice maker is totally different system. No clicking when push ice button but ice in bulk tray may mean the simplest of malfunctions: Ice bin not pushed in the last half inch if ice auger not lined up with drive pegs. There are hidden switches behind ice bin that need to be engaged or nothing will happen in the ice maker: no auger noise, no clicking, no new ice making. Ice bin will be flush with sheet metal if it is in the right spot. Also plastic juice rack won't hang properly if ice bin not pushed in all the way.

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If it's cooling ok, they're probably normal sounds. Modern refrigerators can make many noises, most people aren't home long enough to hear them. A popping sound could be defrost water hitting a hot defrost element, or refrigerant making noise in the cooling lines. If it's working ok, ignore it. Please rate this,Thank u

sputering and gurgling is a common complaint with lots of models. it is the surculation of the refrigerant thew the evapurator tubing behind the rear wall. make shure the units condensor underneathe the fridge is clean and clear of dust. it can cause the head preasure from the compressor to increase witch can cause excesive sound in circulation. hope this helps you

sounds like you need a new fan motor or blade