Helga Blabs It All / Harold the Butcher - S3-E1
Audio problem: Helga Blabs It All: When the boys hear the ice cream truck from outside, they all start running and saying, "Ice cream," but none of their mouths are moving. (00:08:48)
Curly Snaps / Pre-Teen Scream - S3-E6
Audio problem: Curly Snaps: At the start, Curly talks to Arnold about how good it is to be ball monitor. When Arnold says, "Well, I never thought of it that way," his mouth stops moving after the word "it." (00:01:25)
Curly Snaps / Pre-Teen Scream - S3-E6
Audio problem: Pre-Teen Scream: When Phoebe turns on her CD player and reveals her Ronnie Matthews posters in her room, she says, "Now to compose the winning contest entry," but her mouth isn't moving at all. (00:13:00)
The Aptitude Test / Oskar Gets a Job - S3-E9
Audio problem: Oskar Gets a Job: After Oskar comes home after delivering the newspapers, as Arnold asks him, "Did you deliver the newspapers?", his mouth says, "Did you," but it never says, "deliver the newspapers?" (00:22:08)
The Aptitude Test / Oskar Gets a Job - S3-E9
Audio problem: In the comic book shop, Gerald says "Ho. Touche, sir." but his mouth doesn't move at all.
Arnold & Lila / Grand Prix - S3-E13
Audio problem: Arnold and Lila: Near the start, Arnold tells Stinky, "I like Lila, but I don't like her, like her." The camera cuts to a different angle before he says the last "like her," but his mouth doesn't lip sync the words. (00:01:21)
Helga's Show / The Flood - S3-E15
Audio problem: The Flood: When the kids go into room 315 looking for Mr. Simmons, Arnold calls out his name, and his mouth does not move. (00:20:24)
School Play - S3-E19
Audio problem: Before the play begins, when Mr. Leichliter tells Mr. Simmons, "It's going to be a fiasco," his mouth doesn't move until the shot changes mid-sentence. (00:19:12)
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.