When Scout rolls into the Radley front yard in the tire in Chapter 4 of To Kill a Mockingbird, what does she hear?

In chapter four in To Kill a
Mockingbird, Scout, Jem and Dill are trying to think of something to do.
Summer has come once again and the children are trying to find a way to entertain
themselves. Jem says that he will push Scout in the tire. Jem pushes her really hard and
she goes rolling right into the Radley yard. Scout is stunned by the jolt and doesn't
realize at first where she is, then the yelling from Jem shakes her out of it and she
runs out of the yard. 

Jem, Dill and Scout start playing a
game about Boo. Scout isn't really into it, but she doesn't want to be left out, so she
goes along with it. When Atticus comes along and catches the children, he is very upset
with them. He warns them to stop playing the game and to leave the Radleys alone. Scout
is glad her father came along.

readability="11">

Atticus's arrival was the second reason I wanted
to quit the game. The first reason happened the day I rolled into the Radley front yard.
Through all the head-shaking, quelling of nausea and Jem-yelling, I had heard another
sound, so low I could not have heard it from the sidewalk. Someone inside the house was
laughing.

When this happened,
Scout begins to realize that Boo is actually watching them. The children have spent so
much time trying to find a way to see Boo, but Boo is the one who is watching them. Jem
and Scout should be very thankful that Boo is watching them, in the near future they are
going to need him.