SRAM Eagle XX1 Cassette creaking under torque, only after warming up

The most common cause of this with XD cassettes is simple under-torquing of the "lockring"/locking sleeve/whatever you want to call it. SRAM's number is 40Nm. The sleeve turns with quite a bit of resistance inside the rest of the casssette on XD cassettes, which can lead to not having it actually tightened on right as the friction is eating up torque before correct thread preload is established. You can run a bit of lube down around the sleeve to mitigate that.

If it's not that, and assuming this is some kind of fairly typical cartridge hub, if you're saying there's essentially no change after the steps you've already taken, here's what I would do:

• Confirm you can't make the nosie occur when rocking the wheel back and fourth laterally as though to check for bearing play.
• Confirm everything is in good condition, clean and properly lubricated with the dropout/hanger. Or just take the wheel out, poke the bare axle into the dropout, reef gently and corrobrate you can't generate any noise.
• Corroborate the drive side main hub bearing is in good shape, externally clean and lightly greased, if you didn't already do that when replacing the freehub body.
• With those things crossed off, and again presuming you mean to say there was zero change with a new freehub body, it becomes difficult for this to be anything but a movement that's occuring within the construction of the cassette itself. If there's no obvious problem, then what I would do next is take it off and give it a bath with whatever you have handy. If nothing else you can soak in boiling water and a squirt of dish soap, then air dry on a towel. You're not necessarily trying to fix it here, but cleaning it will probably change the noise enough to diagnose. If this route gives you anything, I would suspect a little it's the integral XD "lockring" component of the cassette, and could perhaps be fixed or mitigated by getting some lubrication worked into the interface between it and the rest of the cassette once its clean.

So after replacing the free hub and didn't help, I looked closer and realized the creaking was happening at the little spline fingers that flare out on the outside of the cassette to hold it in place. Grease did nothing to help, so I finally bought a new xx1 cassette.

And wouldnt you know it- the new(er) xx1's (xg-1299's) went to the same lock ring designs that the lower models have always had. I guess the one piece fingers version was creating some problems, possibly just like the issues I encountered!

New cassette works great, would have been nice to know this one had a design flaw earlier on as it had been making some noises almost from the day I bought it, and would have had the cassette warrantied if had known this was the problem. I rode it this way too long and now the warranty is expired. yay.