The knocking noise is coming from inside the compressor unit,it lasts for aboat 5 to 10 seconds,sometimes a full minute.fridge is 5 years old.had this problem for the last year.

https://www.youtube.com/watch?v=sLR2vKxgwbM

A freezer compressor is what pumps chilled Freon -- or another cooling agent -- through coils that line the freezer compartment. ... The cooling agent inside the compressor is sensitive to being moved around, which can cause knocking noises. Also, loose components can cause knocking sounds.

Check the fan isn't hitting a build up of ice in the box

Pull the fridge away from the wall and inspect the compressor. Your description sounds like the compressor is hitting something. It is rubber mounted and usually can be pushed away from whatever it is hitting.You do not want to jamb something to stop the noise, as the compressor needs to move freely. Many compressors shake during start up and shutdown, and this is considered normal. Abnormal if the compressor hits something during this movement.

The knocking noise will be from the compressor in the back of the fridge. It is a (typically) black object a little smaller than a soccer ball, situated at the bottom of the unit in the rear). It will have pipes connecting it to the hear exchanger (a black radiator that covers most of the rear of the fridge). The knocking will happen when the fridge is in a cooling cycle and the compressor is running.

There are 2 reasons for the compressor to "knock":

1) It is positioned on rubber mounts and one of these may have become dislodged if the fridge was moved recently. Or one or more of the mounts may be worn, or the compressor may have been slightly moved by something and is knocking on another component or the chassis of the fridge. It may be simple enough to check this out and move the compressor on its mountings slightly to aviod the knocking.

2) Far worse, the knocking may be from an internal component in the compressor. Sadly, this is a sealed unit and while it is possible for a professional to replace the compressor and then re-gas the fridge (Re-fill the coolant gas that will escape when the compressor is removed), the cost of doinf this will probably mean that the fridge is beyond economical repair.

If it seems to be coming from underneath the unit it could be the compressor. Normal 0 MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman";} That's usually mounts inside the compressor. Usually when the compressor cuts off. It could still last awhile so if you can put up with the noise just wait for it to quit before replacing the compressor or getting a new fridge.
Any other noise would be from a fan. One in the freezer behind the back panel and one under the unit where the compressor is.

If the noise is actually from the compressor then the spring inside is broke and the entire compressor needs replacement. Usually a $500.00 job.

sounds like the compressor vibration dampers are wearing out. the dampers are the rubber washers that seperate the compressor from the chassis of the fridge. when they start to deteriorate, and the compressor kicks on, it will bounce against something in the chassis, causing a knocking noise.

I also have a new Whirlpool Gold fridge (bottom freezer with French doors) and it was making a knocking sound. The knocking sound would start when the fridge kicks in and starts running to cool, and would last for about a minute or less and be a slow knock.
I called Whirpool customer service since it is new and on warranty. They sent out a technician and he said the knocking is from gas/air built up in the copper tubing for the freezer because the copper tubing is too cold, and when the fridge first turns on it forces the air through, making the knocking sound.
His "fix" was to adjust the copper tubing so that it is closer to the heat of the motor/compressor and heat of another copper line so that the cooler line stays warm so the air/gas doesn't build up. His fix worked slightly, but the fridge is still knocking, just not as bad and not as long - it knocks fast for about 5 to 10 seconds instead of a minute.
Going to call customer service again soon and see where to go from here.

heres a part number for the overload relay assy 5304468029.. its mounted on the side of compressor. its a tricky one, usually my experience has been the noise comes from a bad compressor( which you should have 5 year full warr from manufacture). sometimes the overload relay does go bad preventing compressor from starting,the n ew compressor will come with a new overload relay

if you have ice buildup then the fridge may be low on freon.
or there is dust clogging around the pump or fan is not running.
remove the bottom or back and look around the compressor.
see that the fan is running.