[Rory walks up the porch steps]
LORELAI: Hey, uh, Dean called twice.
RORY: Rah, rah, rah. [goes into the house]
Rah, rah, rah is a typical cheerleader chant meant to create greater enthusiasm and excitement. Rory says it very snarkily.
Also note that Rory has only just had coffee with Dean, and had a short interaction with Lane on her way home. By the time she’s walked back to her house, Dean has already phoned twice before she even gets in the front door. That seems worryingly insecure, and even rather controlling. Rory’s ironic cheer may be a sign that she doesn’t welcome Dean’s constant calls.
The Annotated Gilmore Girls 