Quiche filling sets like an Aero bar?
Are you just using eggs for your filling?  Most quiche fillings are a custard, with milk, cream, or other dairy as well as eggs, and often cheese as well. 

It sounds like you are over beating your egg or custard mixture, and inadvertently incorporating air.

In general you want minimum air in a quiche filling, so whisk or stir it briefly until it comes together, but not extra.

Its harder to tell from the description, but you may also be over baking the quiche.  You want to cook it until the center just barely jiggles, about 180 F / 82 C.