I think it's a bug with the audio. I recommend reporting here: https://support.duolingo.com/hc/en-us/requests/new
Why is 'Dauud' not accepted as a rendition of the Arabic letters equivalent ? Why must it be 'David' ? Or is it simply a case of the contributors' trying to impose their personal bias on us all ?
I think it's Dawud, because the و can be both a 'w' and an 'u'
Maybe they wanted to point out similarities between westerners and Arabs