Just this monday I started noticing a fairly loud squeak coming from what I assume is my cassette, but it could be coming from my crank as well (which is odd, because I didn't change anything between sunday and monday). It only happens when I'm in my 3rd, 4th and 5th smallest cogs (why I think it must be from my cassette), which I find peculiar. And it happens when I put the gas on (as in 2 squeaks per revolution of the crank). I have a SRAM OG1090, which I know is supposed to be loud when shifting, but I don't think this is normal behavior. I've adjusted the RD a few times, but still can't get rid of the creak. The way this cassette is made is the largest 7 cogs are one solid block, and the smallest three are separate–maybe this has something to do with it? Any help would be greatly appreciated!

Tightened the lockring?

Ah actually you might be right. I just checked my cassette and it turns out the smallest two cogs are not connected, which makes sense with a loose lockring. Those outer 3 cogs would produce the most torque (being furthest from the base of the cassette), so if the cassette was a bit loose, they would be the prime suspects for the squeak. As it turns out, my cassette wasn't quite at the 40 nm it was supposed to be (maybe more like 15), so hopefully this fixes it! I'll find out tomorrow.