DIAGNOSIS This is usually an HDMI CEC or eARC handshake issue, not the TV's internal speakers.
FIX Go to Settings > Display & Sound > Sound. Turn off 'eARC' and 'HDMI CEC'. Restart the TV. If the sound is stable, turn them back on one at a time to find the culprit.
IF THAT DIDN'T WORK The TV's audio output format may be mismatched. In Sound settings, set 'Digital Audio Out' to 'PCM' instead of 'Auto' or 'Dolby Digital'.
HEADS UP If using a soundbar, connect it via optical cable to bypass HDMI handshake issues entirely. Update your external device's firmware.