ertönen
to sound / ring out
The sudden or clear becoming audible of a noise, melody, or signal.
Als der Vorhang aufging, ertönte lauter Applaus im Theatersaal.
When the curtain went up, loud applause rang out in the theater hall.

to sound / ring out
Loading your saved state.
to sound / ring out
The sudden or clear becoming audible of a noise, melody, or signal.
Als der Vorhang aufging, ertönte lauter Applaus im Theatersaal.
When the curtain went up, loud applause rang out in the theater hall.

'Ertönen' (to sound/ring out) is an inseparable verb. The prefix 'er-' always remains attached to the stem 'tönen' (to sound). Here it signals the beginning or sudden occurrence of a sound.
Plötzlich ertönte ein lauter Knall.
Suddenly, a loud bang rang out.
The perfect tense of 'ertönen' (to sound/ring out) is always formed with the auxiliary verb 'sein' (to be). The reason is that the verb describes a change of state—from silence to sound.
Pünktlich um zwölf Uhr ist die Sirene ertönt.
Right at twelve o'clock, the siren sounded.
The subject of the verb 'ertönen' (to sound/ring out) is always the sound itself or the source of the sound. People or animals cannot 'ertönen'.
Aus der Ferne ertönte leise Musik.
Soft music sounded from the distance.
Common subjects for this verb are signals and sounds. Typical examples are: a signal, a melody, a call, applause, a bell, or a siren.
Als der Sieger ins Ziel kam, ertönte die Nationalhymne.
When the winner reached the finish line, the national anthem rang out.
to sound
'klingen' and 'ertönen' can both describe that you hear a sound. 'klingen' is very general and often describes how a noise or music sounds. 'ertönen' puts more emphasis on the moment when a sound suddenly or clearly becomes audible. It sounds somewhat elevated and fits well with signals, music, or loud noises. The words can be confused because both have to do with hearing. If you want to describe the quality of a sound, use 'klingen' rather than 'ertönen'; if a sound suddenly begins, 'ertönen' fits better.

Plötzlich ertönt ein lautes Signal im Bahnhof.
Suddenly, a loud signal rings out in the train station.
Aus dem Radio klingt leise Musik.
Soft music is playing from the radio.