For me, the biggest culprit in my 3 previous profile rigs was always the seat sliders. So much so that I ended up removing them a couple of times which fixed the issue, but was a pain for obvious reasons. Thankfully, for whatever reason (or maybe because I applied a decent amount of grease first), this set of seat sliders has been fine. When I set the active pedal to a formula profile, so really stiff braking, the seat itself will make some noise if I have to brake at max pressure, but not a lot that can be done about that. For GT driving, it's not an issue
But yeah, have a look at your seat sliders. Overly tight bolts, not tight enough bolts, or even a lack of lubrication can all lead to creaking