There is also an Underdog episode with the same name.
Originally, the episode was going to be the 619th episode of the series, but it got bumped up to 620 with the announcement of Springfield Splendor, which itself would later be moved to an October 8, 2017 airing after The Serfsons was chosen to be the season 29 premiere.
This episode uses the old Season 3 version of the theme song, which features violins playing (to make them sound like the "Ahh" choir) instead of the synthesized "Ahh" choir. This is one of the newer episodes to use the old Season 3 version of the theme.
Oddly, in one scene, two cribs can be seen in Maggie's room. The other crib cannot be seen at any other point.
While Homer plays Peekaboo with Maggie, a green toy swing set can be seen in front of the window. Later, when Homer is looking around for the person who is whistling, it has disappeared.
Despite the flashback stating that Abe can no longer whistle, Abe is then seen whistling professionally.
So it must mean that his mouth got healed since that.
Alf Clausen is credited in the closing credits for this episode despite being fired from the series.