The Chaperone / Employee of the Month - S1-E12
Audio problem: We see Spongebob in his long legs walk over to Mr. Krabs' house, then we see the door from inside the house. Through the window we see Spongebob's long legs, yet we hear him spring boing his way over when we see them already there.
Answer: I believe this is the Season 6 episode "Spongicus".