I have the Z Flip 4 and one day last week my screen protector peeled off in the middle. When I opened my phone it unstuck, making a sticky cracking sound similar to what you describe.
You can get one free screen protector replacement from Samsung and maybe an idea would be to get that done, to see if that is the problem. However, beware as I've heard if the screen is damaged it's costly to replace unless you have insurance and it's possible (although unlikely) when removing your screen protector they could damage the screen and say it was already damaged. Lots of reviews say this online; I discovered these when I looked up replacing my screen protector before deciding if I wanted to use that free service or not.
[I decided not to and replaced it myself, which was easier than I expected. I figured I'd take more care than perhaps a trained technician would with lots of them to do... you can decide if that's good judgement call or not, but for me it worked out.]
Alternatively, send your phone in to have it examined and repaired if needs be, especially if you have insurance.
Other than that, I've not heard of unsticking/cracking sounds, unless the screen itself is delaminating? You should be able to see this by looking at your hinged part of the screen though.
PS In case this is useful info, the screen protector I used to replace the original Samsung one was from the company Whitestone, on Amazon for £15.99. I watched a few YT videos before attempting it myself and used one as a step-by-step guide as I replaced it.