For FPFU19F8WF4, a loud gurgling/“glug-glug” noise immediately when the door shuts usually points to the drain system or pressure equalization, especially since there’s no ice buildup and the door gasket looks good.
Quick test first
Open the refrigerator door for 20–30 seconds, then close it while listening near the bottom rear of the refrigerator.
If the gurgling comes from that area and lasts only several seconds, check the defrost drain tube and drain pan first. A partially restricted drain can make surprisingly loud gurgling as pressure changes when the door closes.
What I would check
Defrost drain
Locate the drain opening beneath the evaporator area.
Pour a small amount of warm water into the drain.
It should flow freely into the drain pan underneath the refrigerator.
If it drains slowly, backs up, or makes excessive bubbling/gurgling, clean the drain tube.
Don’t assume the drain is clear just because there’s no visible ice.
Drain tube at the bottom
Pull the refrigerator out and remove the lower rear access panel.
Find where the defrost drain tube terminates above the drain pan.
Check for debris, slime, or a partially restricted rubber drain fitting/check valve.
Clean it thoroughly.
Listen at the door
Close the door and determine whether the sound is actually coming from the door/gasket area rather than underneath.
Refrigerators develop a slight pressure difference when the door closes. Some brief air movement is normal.
A new or increasingly loud noise isn’t something I’d automatically dismiss as normal.
Listen for refrigerant noise
If the sound comes from inside the cabinet/evaporator area and continues independently of opening or closing the door, refrigerant flowing through the evaporator can produce gurgling.
Refrigerant gurgling by itself can be normal, particularly when the compressor starts or stops.
But if cooling performance has also changed, then we’d want to investigate the sealed system further.
One useful isolation test
When it’s quiet, unplug the refrigerator for about 5 minutes. Plug it back in, but immediately open and close the door before the compressor has had much time to operate.
Still gurgles specifically when the door closes: I’d concentrate on the drain/air-pressure system.
Only gurgles while the compressor is operating or shortly after it stops: refrigerant movement becomes much more likely.
Since you say this is getting progressively worse, I’d start by checking and flushing the defrost drain and the drain outlet underneath. That’s the first thing I’d want to eliminate before considering it normal refrigerant noise.