If it happens again, please leave the T8S on, and turn off the L1® that is silent. Disconnect the power cable.
Reconnect the power cable and turn it back on again after a full two minutes. It should only take two minutes for the unit to reset.
If the sound comes back, then we've isolated the issue to the L1® (not the T8S). If the sound doesn't come back, on the T8S - turn the power off/on. If the sound comes back then the issue is the T8S.
Please let us know if it happens again and what you discover.