In September 1988, Looney Tunes aired on Nickelodeon until September 1999. The show also aired on Nick at Nite from 1988 to 1992.
It featured a different intro and at the beginning shows a clip from "A Cartoonist's Nightmare" where the cartoonist says "Hoo-hum, I'm tired" and shows clips of Looney Tunes shorts set at the nighttime. Then the cartoonist draws the Looney Tunes on Nick at Nite logo at the end.
The intro was on Dailymotion but was removed. It was finally found on YouTube but it was removed once again due to copyright infringement.
The intro has now been found by CDCB2 and hopefully it don't get taken down again. Link to: https://www.youtube.com/watch?v=0euouI6jV4Y