One of our comments on the latest Tech Spotlight pointed out we didn't touch on the cassette - and JaseRidesBikes was absolutely correct so here it is!
We're going to touch in specific on XX1 Cassette installation and where we have commercially found creak issues.
The number one issue for creaks on these cassettes is FALSE TORQUE. The XD driver interface has substantial contact friction in the system, which leads riders to feel that they have torqued the assembly correctly when in fact the cassette is still loose on the driver. The lube and grease steps shown here are not to mask creaks - they are to reduce contact friction during assembly to allow a proper torque of your system.
NOTE: If you have questions don't destroy a cassette or driver. Work with a qualified resource as needed.
SRAM is aggressive with their running changes. This is a brand new cassette and has the internal threads pre-greased from the factory, the initial run cassettes did not come pre-greased.
If you are reassembling a 11 speed system insure that your cassette / driver are lubricated in the areas shown below:
The cassette fastening system should be lubed prior to assembly to minimize contact friction. Feel the friction in the fastening system prior to and after lubing the three points shown in the photo - it typically is quite notable. Joe is using TriFlow wet lube in the photo below.
It is critical that the XX1 cassette seats completely flush when torqued. Taking the steps above should minimize your contact friction during assembly. You will not need Herculean efforts to torque the system down if done correctly - however there is a decent amount of torque required to set the cassette in. Review the SRAM torque specs as needed.
Check your cassette to insure that there is not play in the system. If you have torqued the assembly AND have play there is an issue - depending on your problem solving skill set it may be best to contact a more qualified resource.
Again the lube and grease are not designed to mask your creaks - simply to allow the system to torque down correctly. If you have been suffering creaks in your 1x11 cassette I would wager 9 of 10 are from systems that are not correctly tightened down.
Some other issues we have seen: poor driver tolerance may not allow the cassette to interface properly. It is easy to eat up threads if you apply monster loads to something that is not going to physically fit.
Authors Note: The first XX1 cassette I installed for myself did not seat correctly (I'm the GM here not a mechanic...) but the false torque led me to believe I had it nailed. When I went to install the wheel the 10 tooth cog was in contact with my carbon rear triangle, which I caught in the stand prior to destroying anything, but it was a bit confusing / irritating. Our mechanics showed me the above and I haven't had issues since... Also - with the extra torque on the 42t make sure you use a hub designed for the increase load the larger diameter exerts.