e*thirteen cassettes are designed for long term, quiet operation. However, like most high-precision bicycle components, periodic maintenance is required for best results.
Most cassette creaking noise can be resolved by disassembling the cassette, applying a liberal coat of grease to the contact points between the steel and aluminum pieces, and re-assembling. Also it should be verified that the cassette end bushing is installed between the end of the XD driver and the pocket in the steel section of the cassette.
Here are the locations you should grease:
Check out one of these articles to see how, depending on your cassette:
Cassette End Bushing
All current e*thirteen cassettes use a teflon filled Delrin bushing to support the steel portion of the cassette. If this bushing is left out during assembly, your cassette will creak, and may be damaged!
It's a good idea to check to make sure this bushing is installed if you're getting persistent loud creaking from your cassette.
If you have a 9-42 10-speed or 9-44 11-Speed cassette, please see this article: My TRS+ 9-44 cassette is creaking, how can I fix that?