Hi @jjlink
Welcome to the Sonos Community!
I’d like to look into this issue for you, but I am not 100% sure what you mean by “fluttering” - could you please elaborate? Thanks.
If you mean they play but with repeated audio interruptions, please try removing the surrounds from the Arc Ultra and add them back on again.
Remove surround speakers
Add surround speakers to a Sonos home theatre
If this does not resolve the issue, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.
I hope this helps.
"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein