It's even weirder that when you slow it down (the turtle button), it does says "die" 0_0
No, you're not alone. It's the old geezer at work again. Someone please put him out to pasture...
Yeah, it seems to be a problem with the audio.
As you've just said, the correct way is ''Die weiße Katze.''
No. It would be "Die weißen Katzen" as this is in the nominative case, plural, and due to the definite article "die", the adjective takes weak inflection. Thus you add an -n at the end of the adjective. The adjective now corresponds with the noun in number as well, indicating that many cats are the subject as opposed to a single cat. Please feel free to correct me :-)