If you hear it in DVD-A, when playing back, that's a good question.
Did you prepare your files using DVD-A? Because I've never, ever had a prepare fail, if they play in DVD-A
Now, you can manually import both files separately in DVD-A. You need to Double click on your video while on the 1st menu page of DVD-A, this will take you to the Media section where you add chapters and you see both the video and audio in the timeline near the bottom of DVD-A.
In the Media properties, to the top and right of video screen, the 2nd tab down is called 'Track Media', Highlight that and you'll see the video and audio in white section an inch or two down. On the right of either of those, if you hover your mouse on the title and left click, an option will open allowing you to swap out either your video or audio.
From the bottom of this same page, you'll see normal 'Play' controls. If your video plays and you hear sound at the same time, you're ready to 'Prepare' your DVD. Unless you want to add chapters.
Now hit the 'up' arrow, 3 Icons to the left of the magnifying glass near top right of DVD-A screen. This takes you back to the 1st Menu page
Then 'Make DVD' button, top center.
You can simply Prepare it, to be burned by another program or
You can Prepare & Burn it with the center button and DVD-A should complete it, although some other DVD burning programs won't let DVD-A burn. Like my Nero, won't let DVD-A have access to the burner. So I burn my prepared files with Nero, but they were prepared for burning by Vegas
Normally, the preparing mixes the audio and video files together and puts both in the 'VIDEO_TS' folder. The AUDIO_TS file is empty, but some burning programs need both folders anyway.
If you 'Prepared' using anything else, I probably don't have a clue what to tell you. As I said, I've never had a 'Prepare' in DVD-A go bad. I've even successfully had two audio tracks I could choose from.