Does it happen as soon as you begin that event, or is there a certain point in the event where the sound is triggered? And is it in the full event only or does it also appear when replaying that room from the blueprint screen?
If it started more or less at the beginning, then it may be bleed over from some other event. In that case, I'd try completing some other event first to clear the audio channels.
If it still persists, try using your device's speakers or a different audio output device and see if that changes anything.