How does Miller create a dramatic climax at the end of Act 2 in Death of a Salesman?

Miller creates a dramatic climax in Death of a Salesman at the end of Act II through the use of music, leading to loud music to simulate the car crash.

As the play ends, we see that Willy has been trying to decide if he should commit suicide to provide his family with the insurance money.

The stage directions clearly indicate how music is used to create suspense as the play reaches its exciting climax in Act II.

Suddenly music, faint and high, stops him. It rises in intensity, almost to an unbearable scream. He goes up and down on his toes, and rushes off around the house. (Act 2, Scene 6)

As the music gets louder and louder, the play gets more and more exciting.  We know that Willy is about to do it.  The music tells us so.  The music and sound effects of the crash create a primal response in the audience (and help the reader picture it).

What foreshadowing details does Miller use in Death of a Salesman?

At the end of the play, Willy will commit suicide through a car accident so that Biff can get a fresh start in life with the insurance money. This end is foreshadowed through the following details. When Willy comes in late, Linda asks him if he had a car accident, because he once did by driving off a bridge. He says no, but he does say he was going in and out of a trance when driving. This establishes that Willy is not always the best of drivers.

Willy's suicide through a car accident is also foreshadowed when Willy says to his neighbor, Charley, while borrowing the money from him he needs to keep the family afloat:

Funny, y’know? After all the highways, and the trains, and the appointments, and the years, you end up worth more dead than alive.

As a traveling salesman, much of Willy's life has been spent on the road. He has not been very successful on the road, but it makes sense that he would eventually try to make his time in a car pay off, even if in a self-destructive way.

That almost nobody will come to his funeral is also foreshadowed earlier in the play. Willy thinks of a successful and well-loved salesman he knew who had a huge funeral. However, by Willy's own admission in his honest moments, people don't like him much, something we can easily understand as he is always trying to one-up and impress people to counter his own insecurities.

How does Miller's opening in Death of a Salesman foreshadow the play's tragic ending?

Willy comes back home unexpected since he had just set off a few hours earlier on a business trip. He doesn't want to tell his wife Linda that he has wrecked the car (again!), but he finally explains that he can't keep his concentration when behind the wheel and just steers off the road.  He mumbles something too about having "terrible thoughts" and speaks of being "tired to death."  These incidents and comments are a foreshadowing of Willy's "accident," as the spectators already see that Willy feels tired, old, and overcome by a situation (as the car) gone "out of control."  Willy's suicide is ironically the only way he can assume his role as a responsible husband, father and breadwinner, since his death (by the insurance money it will bring in) will assure that his family is at last provided for.