Sonos Arc Ultra + Sub Gen 4 – Severe HDMI eARC Sound Issues with Hisense and LG TVs

Hey everyone,

I wanted to jump back on here and give a massive thank you to everyone who jumped in to help me troubleshoot the issue with my brand-new setup.

For context, my LG 55QNED86B (bought Oct 10th) and my Sonos Arc Ultra (bought last month) were locked in a brutal loop where the volume would automatically force itself down to zero every 10 seconds. Even if I manually turned it back up, it would cut right back down to zero. It made watching normal TV, Netflix, and Prime completely impossible.

Thanks to the advice here, I finally got it sorted! If anyone else runs into this nightmare with a brand-new setup, here is exactly what fixed it for me:

• The System Updates: Because both pieces of kit are brand new, the firmware versions were completely out of sync out of the box. I forced a fresh update through both the Sonos app and the Fire Stick, alongside a webOS system update on the LG TV to get all their communication channels aligned.
• Changed Fire Stick Format: I went into the Fire Stick's internal display and sound settings and locked the audio output format down to Dolby Digital rather than leaving it on an unrestricted auto setting.
• Disabled TV AI & Energy Settings: I went into the LG settings and turned off "Energy Saving Step" (which was aggressively throttling power to the HDMI ports). I also disabled "AI Sound Pro" and "AI Acoustic Tuning" so the TV stopped fighting the Arc Ultra's native audio processing.
• The "Ghost Signal" Check: I completely removed the batteries from my remotes to ensure a stuck IR button wasn't spamming a volume-down loop, and checked for any unpeeled protective factory plastic film near the TV's IR receiver.

The audio is now perfectly stable, holding its volume, and sounding absolutely incredible. I was even looking into buying a hardware middleman like the HDFury Arcana, but thanks to your guidance, I realized my TV's native eARC port handles everything perfectly once the software bugs are squashed.

Cheers again for the brilliant support—much appreciated!