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https://www.dailymail.co.uk/science...-source-loud-sounds-haunt-kitchens-night.html
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https://www.realtor.com/advice/home-improvement/refrigerator-making-noise/
It's hard to specifically define a "thWHACK" sound. Can you record the sound @ the back of your fridge and posted it ... like on YouTube for example?
All fridges of course make noises. I would love to get a "completely silent" fridge, with noise suppressor, quiet compressor, ...all that jazz.
In the first link above (it's a very good one because it explained what I've learned on my own over the years) the outside temperature has an influence on fridge noises and much more.
You live in a condo, with perhaps AC and well regulated temperature; so it shouldn't affect you...I think. But it's an educative article nonetheless.
The second link might help you.
I am not a fridge expert; I've heard fridges from various price brackets and they all have their unique sound (noise) with the kitchen own room's acoustics. But the "thWHACK" sound (noise) you just described might be somewhere in that second link.