In addition to the incidents clairewait points out, the incident at the beginning of Chapter 15 (prior to the scene outside the jail) is a good indicator of tension and unrest in the town.
After dinner, Jem answers a knock at the door, and tells Atticus that Heck Tate is there to see him. When Atticus tells Jem to invite Heck in, Jem reports that there are other men with him and that Atticus should go outside. Though the children only hear bits and pieces of the conversation, they understand that the men are discussing the Tom Robinson trial and gather that the men are warning Atticus of trouble.
Scout, who notes that "In Maycomb, grown men stood outside int he front yard for only two reasons: death and politics," wonders who has died; unlike Jem, she is unable to understand the scope of the situation. As the men get closer to Atticus, Jem screams that the phone is ringing, because he senses trouble. The men laugh, and eventually depart, but Jem, who has been watching intently, says to Atticus, "They were after you, weren't they? They wanted to get you, didn't they?" Atticus replies by telling Jem that those men were friends. Still, it is clear that Jem understands the tension of the situation.
There is tension and unrest in both the Finch household and the town. I think this is important, as the story teller is greatly affected by both.
Starting in her own house, Scout begins to notice, with the arrival of Aunt Alexandra, that things are different. Atticus seems to have less patience and time for her. Jem is even distant, as if he too senses the stress that is affecting everyone. Scout is young, so she definitely notices this tension but probably cannot name it, nor fully understand it.
Then, in Chapter 14, Scout reports in the very first line:
Although we heard no more about the Finch family from Aunt Alexandra, we heard plenty from the town.
It seems the entire town is talking about the trial - from the recognition of "his chillun" (meaning Atticus) to Scout hearing the word "rape." The usual gossip of a small town has basically all turned on the same subject, and Scout not only notices it, but goes home to discuss it with her father. This only furthers the stress at home and reinforces the tension.
In addition to the examples mentioned in the previous post, a crowd of Maycomb citizens congregated on Atticus' lawn two nights before the trial. In addition to Sheriff Tate, others present included Link Deas, Mr. Avery and Dr. Reynolds. The scene is told from Scout's perspective, and she stayed indoors and was not able to hear much about what was said. But Scout knew it must be serious.
In Maycomb, grown men stood outside in the fron yard for only two reasons: death and politics. I wondered who had died.
Scout was able to overhear a bit of Sheriff Tate's conversation, however. She learned that Tom would be moved to the county jail the next day, and that there might be trouble. Then she heard Atticus question the sheriff if he was " 'scared of that crowd...' " The tension became so strong that suddenly
Jem screamed, "Atticus, the telephone's ringing!"
When Atticus finally came inside, Jem revealed that he thought the group of men in the yard were a gang who had come for Atticus. Later, Jem revealed to Atticus that he was scared:
"Scared about Atticus. Somebody might hurt him."
There is tension in the Finch house because Aunt Alexandra has arrived and her views conflict with those of Atticus. She believes the children should follow the mold society has set and does not view everyone the same. Another is when a mob came for Atticus and Jem pulled him inside the house by yelling that the phone was ringing. He was worried about Atticus as well.