Match Frame. Make sure the Auto-Select buttons (black dots to the right of the track names) for the video tracks are on. Put the playhead on the video clip, select the clip and press F. This will call up the master clip into the Viewer, which should have the audio attached. Drag back into the timeline or use Replace Edit.
Oh, and next time you edit and you're not sure whether you want the sound, try disabling it rather than deleting it. Select the sound and press CONTROL-B (Clip Enable/Disable).
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