11/2007 "30 Rock":

While the maple syrup smell remains a two-year-old mystery to us, 30 Rock entered the fray with a hypothesis. On last night's episode, Liz Lemon, who smells waffles from her Upper West Side apartment, calls Tracy Jordan to remind him to practice his Re-Run dance for the What's Happening! sketch. But Tracy, in his NJ home, says that the smell of waffles is distracting him. Then Liz gets another call - it's Jack Donaghy, over on the Upper East Side:

Jack: Do you smell maple syrup?
Liz: Yes!
Jack: Don't panic, Lemon, it's probably not a chemical attack.
Liz: What do you mean, probably?
Jack: It's probably just a strange wind pattern coming over those factories in Staten Island where food flavors are made. I don't think it's northrax.
Liz: What's northrax?
[Tracy starts his Re-Run dance]
Jack: It's a chemical agent we sold to the Saudis in the 1980s that smells exactly like maple syrup. But I don't think this is it.

Mystery solved.