Hi, GIGA-Man! Unfortunately the Russian representative who answered my letter told me that I needed to deal with that shady firm directly as it was now responsible for the bad repair job they had done with my card. Basically, as my warranty is now voided, the Gigabyte employees in Russia are no longer responsible for it. I ended up calling a programmer who is an acquaintance of my father, and asked him to take a look at my card. He found out that the cause of the fan problem was the dried up thermal paste (there was practically none left; it had either dried up completely after 6 months of heavy usage, or hadn't been applied properly during the production phase). The middle fan was also missing one of the screws (I don't know whether it was like that when I bought the card or those con artists had something to do with it). The card now works quietly just like it did before January, even on Ultra settings in Red Dead Redemption 2.
Thank you anyway for not ignoring my plea for help. I'm glad that the Gigabyte legal department took notice of that shady "service center". Could you please update the Russian section on
https://www.gigabyte.com/Support/Warranty , to specify that
http://www.gigabyte.ru/ is the correct website for Russian customers to turn to should any problems arise? Right now gigabyte.com just asks the users from Russia to contact the shop where they bought Gigabyte products. I would never have fallen for those scammers if the shop where I bought my RTX 2080 TI hadn't turned down my request for warranty replacement, judging that annoying fan noise "a normal working sound" (which is ridiculous).
The lesson learned: in the future I'll only deal with my hardware problems through official channels.