DIAGNOSIS Classic wireless interference. The Beam is losing its connection to your TV, usually because the HDMI cable is faulty or the Wi-Fi channel it's using for SonosNet (if you have other speakers) is clashing with something.
FIX First, swap the HDMI cable between the Beam and your TV's ARC/eARC port. Use the one that came with the Beam if you still have it, or a certified high-speed one. A bad cable is the culprit more often than you'd think.
IF THAT DIDN'T WORK If you have other Sonos speakers, log into your router and change the SonosNet channel. In the Sonos app, go to Settings > System > [Your Beam] > About My System to see the channel. Change your router's Wi-Fi channel away from that number (e.g., if SonosNet is on channel 6, set your main Wi-Fi to 1 or 11).
HEADS UP Don't just toggle the TV's audio output settings—that rarely fixes this. If you're using an optical adapter, those can fail over time and cause the same dropout, so consider it a suspect.