This is a rare sound effect. It's Warner Bros. Animation's recreation of Sound Ideas, HIT, CARTOON - BRAKE DRUM AND BULB HORN HIT from the Hanna-Barbera Sound Effects Library, utilizing a portion of Sound Ideas, HIT, CARTOON - BRAKE DRUM HIT from the same library and Sound Ideas, CARTOON, HORN - SHORT HORN TOOT, LOW from the Warner Bros. Sound Effects Library. This was made most likely because WBA did not have a copy of the real H-B "BRAKE DRUM AND BULB HORN HIT" in their library at the time.
(a clear rendition combining the two elements of the effect)
(as heard in the cartoon)