Start up animation has not sound on the Omega insider ring

One thing to be aware of, you must be active in the insider program for a while, and be selected for the alpha ring. You will likely start in the "Omega" ring, and after 1 month you can move up to the "Delta" ring. 3 months will get you
into the "Beta" ring, etc.

Instead of leaving the Xbox Insider program as one Ambassador has suggested you can drop down to a lower ring which receives much fewer updates. For example if you are in Beta ring drop down to Delta or Omega. The Omega ring receives the fewest updates,
usually just before it is released to the general public. This can be managed using the Xbox Insider Hub on your console.

Are you in a Insider preview ring?

If so, which ring. ASA, Alpha Beta or Omega?

In my understanding the Dashboard experiment, A, B, C selection, is totally random.

As "Both consoles say their OS Version is (19h1_release_xbox_dev_1911.191028-1335)" your consoles are either in the Beta or Delta ring.

Both those rings and Omega ring are getting a preview update News release notes Beta Delta Omega
Insiders today, which you can manually start or wait until it becomes mandatory.

After you do the update, if you want to change rings, it will be the perfect time to change as all those rings will be on the same release. Subject to eligibility.

In which ring you are? Omega, delta? The right place for question is on insider reddit page.