The Scary Sky Skeleton - S1-E6
Audio problem: During the gang's ride on a bumpy road Fred warns Shaggy, Scooby, and Scrappy about some more bumps coming up. He's interrupted when they hit the bumps, then the word "bumps" comes out of Scooby's mouth.
Scooby-Doo and Scrappy-Doo (1979)
1 audio problem in season 1
Starring: Don Messick, Casey Kasem, Lennie Weinrib, Heather North
Other mistake: When Scooby is eating the hot dogs at the "Hotus Dogus" stand, his tail goes transparent.