We take our noise measurements with the sound meter positioned 1 foot from the graphics card. I measured the noise floor to be 32 dBA, thus anything above this level can be attributed to the graphics cards. The power supply is passive for the entire power output range we tested all graphics cards in, while all CPU and system fans were disabled. A reading under load comes from running the 3DMark Time Spy stress test for 30 minutes.
Of course, the fact that the 6900 XT runs its fans 200rpm or-so faster than the RX 6800 XT, means it is a tiny bit louder, with a reading of 37dBa on our sound meter. To my ear, the noise wasn't noticeably louder than the 6800 XT though, and it's still a terrific result overall.
I do have to mention there was a small amount of coil whine present with my sample, but it was only just audible over my case fans, so when gaming with speakers or a headset on, it simply wouldn't be noticeable.