My freezer builds a thick layer of ice on the bottom

Check for a clogged drain line. Snake out and get some vinegar in there. Any water collecting from the defrost cycle is supposed to be led away and outside from the unit

The ice thicknes control is located on the bottom left. it has a wire going
to it and ha a black rubber bottom. depending on the position it is secured.
will determine the ice thickness. loosen the two screws and push it higher
for smaller cubes and lower for bigger. If you are having problems with it.
There is the possibility it is dirty and sticking.

Very possible the door seal is not properly sealed. Warm inflowing air onto a cold coil will cause ice build up at the lid.

If a freezer ramains shut, it could take 72+ hours to melt the ice.

check door rubber,if is oblate heat it with fan,if it is ragged change it.

One reason for the fan running is that it is trying to distribute the air in the compartment. Look at the very rear of the freezer on the bottom and see if the little vents, which allow water to disperse, are not filled with frozen ice. If so, turn off the fridge (unplug it) and use a hair dryer to melt that ice until it is all gone. That will probably fill the condensation pan under the unit and you'll need to empty it.

There is probably an ice build up behind the plastic rear panel. The ice build up gets so thick that eventually, it obstructs the fan and then you get that loud noise as the tips of the fan are chipping away at the ice.
What you need to do is to remove the rear panel and thaw the ice build up. To remove the rear panel is usually only 2 screws at the bottom.....you will find that the panel is difficult to remove due to ice build up behind it, so gentle heat from a hairdryer is a good way to accelerate the thawing process....once the panel is removed, you will see the ice build up......mine was about 2 inches thick!!!
I used the hairdryer to thaw it all out and then once cleared, switched it back on and have never had a problem since.
By the way, my F?F is a Beko CDA563FS......the one with the water dispenser on the front and frost free.
Hope this helps

defrost drain is blocked - probably with ice. take the back panel off inside the freezer and melt the ice off with a hairdryer then follow up with hot water till it flows away freely. this takes some patience. if fault reoccurs then get back to me

might have the temperature too high .. buy a freezer thermometer and place in freezer

I looked at the BACK at the bottom underneath of my Sears Kenmore frost free upright freezer and what was causing the ice buildup was very simple. At the factory, the assembler looped the little hose too high and when the water went into the hose it could not get out due to being too high in one spot! An ice dam will form, blocking ALL water coming through
and freezing up any more water coming down giving you a HUGE wad of ice that is scary!!! I just removed the screw holding the loop that holds the hose and put a bit of warm water down the little hole on the INSIDE (Behind the grate) to melt the remaining ice in the tube.You need to take out 4 screws and remove the grate to see this. I could not believe that this was the problem! I haven't had any ice build up since.Now don't tear your freezer apart before you try this trying to fix the compressor, thermostat etc. It may be the only thing wrong with it!