Maybe someone else knows a better way but I can only propose a workaround. I will try to explain the issue. When using an interactive object that is pausing the timeline, you'll find under the Options tab the possibility to 'Stop slide audio'. This option is not available for the D&D interaction. You can find and edit the timing of the pause in the Drag&Drop panel, under the Actions tab, but not the possibility to stop slide audio (BTW same is the case for question slides).
My workaround:
- Check the timing of the pause of the D&D slide (Actions tab), default is 1.5 secs
- Insert a click box or a shape button (can be made invisible by changing Alpha and stroke width to 0) on the slide that is pausing the slide at exactly the same moment. It is not meant to be clicked, move it to an impossible place to be clicked.
- For that click box or shape button, check the option 'Stop Slide Audio' under its Options tab. When the playhead reaches the pausing point (which is same for D&D and the click box or shape button) audio will stop.
- Check the Actions for the D&D slide, and be sure to have Continue or to include Continue in both actions; those actions are executed when the Submit button has been clicked, the audio clip will continue now to play.
Not so basic, I know. Maybe I'm overlooking something, but apparently no one else answered your question yet.
I don't understand how you used the Delay command, because this would mean that you need two audio clips, the part before the pause and the part after the pause. Slide audio normally cannot have two clips on the same slide, that is only possible with object audio.