That noise you heard between 2:30 and 2:45 pm EST was the Dow plunging almost 1,000 points in fifteen minutes.

It came back quickly too, but it's still down about 500 for the day…. 

UPDATE:  Oh, this is reassuring….

In one of the most dizzying half-hours in stock market history, the Dow plunged nearly 1,000 points before paring those losses in what possibly could have been a trader error.

According to multiple sources, a trader entered a "b" for billion instead of an "m" for million in a trade possibly involving Procter & Gamble, a component in the Dow.

A typo?  The U.S. Stock Market lost 10% of its value in 15 minutes because some guy made a typo?!?