Details for the final three episodes of Season 3 have been found... and it sounds like another big finish like the previous two seasons.

S3 E24 I Have Heard the Robots Singing: Tensions arise on the team after Doc's new invention causes everyone to sing instead of talk.

S3 E25 Now and Then: The Island of Griffin Rock vanishes from the ocean.

S3 E26 Today and Forever: In order to save Griffin Rock, the Rescue Bots must make the ultimate sacrifice.
Episode 24 sounds like it could be annoying if it doesn't work... as other shows that have had "singing" episodes are fascinating to watch once, but are hard to watch again.