If your 3080 Ti FE is running at 70 during gaming then yeah the fans will not ramp up as loud, my 3080 Ti FE ran the fans up to 2100rpm in games like Cyberpunk. By comparison, the 4090 fans run at 1100rpm in the same game. The 3080 ti FE in my rig also ran at 80-82 degrees too in the same games, I like quieter gaming so my BIOS fan curves are geared towards only ramping up the cas efans if the CPU hits 65 degrees, which it never does in gaming, so in gaming the only fans I hear are the GPU fans, which on the 3080 Ti FE are indeed loud, whereas the Zotac 4090 fans, even in normal fan mode are quieter, but in quiet mode (which is what I am in) are even quieter still. My case is a Corsair 5000D Air with the meshed intake panel, so any noise is audible, but the plus point is its ambient cooling ability is very good as evidenced by my component temps, even with all my case and AIO fans running at 400-600rpm average.
Yeah compared to the 3080 Ti which always felt like it was at its peak labour point when running games especially with RT enabled, even with DLSS, the 4090 just cruises through like as if it's nothing.