meaning of "rattle"

Denise Bauer: Who was that girl I just saw leaving your office? She was, uh, pretty cute.
Brad Chase: Oh, just a friend.
Denise Bauer: Just a friend? You—you dating her?
Brad Chase: Uh, yes, actually. It’s not going anywhere, but—
Denise Bauer: It’s a good rattle, just the same, I bet, huh?
Brad Chase: Excuse me?
Denise Bauer: Do you really think it’s appropriate, Brad? Getting one girl knocked up while you’re dating another?

what's that rattle mean in this context? I guess it is a slang. here are some definitions I have found in dictionary:

"short sharp knocking sounds"?

"noisemaker"?

"disconcert somebody: to make somebody lose composure and feel frightened, worried, confused, or annoyed"?