A Ping is a Ping

[m21man]

How do you play that pinging noise that plays when you complete an objective?

[macguba]

I think you mean the noise when you get a hint.    

Create a trigger:-

Countdown    3    3     3
Condition:    true
On activation:   hint "test"

Is that the sound you want?

[Black_Feather]

Isn't that just a hint,

hint "Objective Completed"