Traders work on the floor of the New York Stock Exchange as Federal Reserve Chairwoman Janet Yellen speaks to the media.

Check out which companies are making headlines before the bell:

Bed Bath & Beyond — The housewares retailer beat estimates by seven cents a share, with quarterly profit of $1.84 per share. Revenue was very slightly above estimates, but the company did give weaker-than-expected guidance for the full year. Separately, Bed Bath & Beyond raised its quarterly dividend to 15 cents per share from 13 cents.

Yum China — The company reported quarterly profit of 44 cents per share, six cents a share above estimates. The restaurant chain's revenue was essentially in line with forecasts. Investors were especially encouraged by an unexpected one percent increase in same-restaurant sales, with analysts having anticipated a drop. Yum China is the China-based spin-off of Yum Brands, and is the parent of Pizza Hut, KFC, and Taco Bell restaurants in that country.

Costco — Costco reported a better-than-expected 6 percent increase in U.S. same-store sales. Analysts had anticipated a 4.2 percent rise for the warehouse retailer, according to estimates compiled by StreetAccount.

Schneider National — The trucking company priced its initial public offering (IPO) at $19 per share, in the middle of the projecting range, valuing the company at $3.3 billion. It's the first trucking company IPO in the U.S. since 2010, according to Dealogic. Schneider will begin trading this morning on the New York Stock Exchange.

MGM Holdings — MGM will buy the 81 percent of the Epix cable channel that it doesn't already own from partners Viacom and Lions Gate for about $1 billion. Viacom owns half of the channel, while Lions Gate has a 31.2 percent stake.

Jazz Pharmaceuticals — Jazz struck a patent settlement with Britain's Hikma Pharmaceuticals related to the narcolepsy drug Xyrem. As part of the settlement, Jazz granted Hikma the right to sell a generic version of Xyrem in the U.S. market.

Cardinal Health — The drug distributor is near a deal to buy Medtronic's medical supplies business, according to a Reuters report. Cardinal would reportedly pay nearly $6 billion for the unit, and the report said a deal could be announced later this month.

Unilever — The Anglo-Dutch consumer products giant has promised a sizable cash return program for shareholders, following its rebuff of a takeover bid from Kraft Heinz. It is also setting a goal of 20 percent profit margins by 2020, compared to 15.3 percent in 2016.

Sunoco — Sunoco is selling convenience stores and gas stations to Japan-based Seven & I Holdings, the parent of the 7-Eleven convenience store chain. Seven & I will pay about $3.3 billion, as it boosts its U.S. operations by acquiring about 1,100 locations.

Twitter — Twitter unveiled a faster version of its mobile service, designed to work better and use less data for those with weaker mobile connections of smaller data plans. "Twitter Lite" would work with a web browser rather than as a standalone app, and Is aimed mostly at non-U.S. users.

Apple — Apple is being sued by Australian regulators, who accuse the company of "bricking" iPhones whose cracked screens were fixed by non-Apple repair shops. The Australian Competition and Consumer Commission said Apple disabled those phones through a software update. Apple has not yet commented on the report.

Amazon.com — Amazon founder Jeff Bezos is selling about $1 billion in the online retailer's stock each year to provide funds for his Blue Origin rocket company. Bezos said his goal is to make Blue Origin a profitable enterprise.

BlackRock — BlackRock said Cisco Systems CEO Chuck Robbins has been nominated to serve on its board. The asset manager said Robbins would join the board as an independent director if elected at the annual shareholder meeting on May 25.

Allergan — Allergan said it will move ahead with its testing of its Botox product as a treatment for depression. The drugmaker said Botox – best known as a treatment for wrinkles – did barely miss achieving a significant improvement in a study, but that the data was encouraging enough to move ahead and begin a larger study.

T-Mobile US — T-Mobile was downgraded to "hold" from "buy" at Deutsche Bank, which said positive catalysts for the mobile operator's shares are already priced into the stock.

Rent-A-Center — Janney Montgomery Scott initiated coverage of the rent-to-own company with a "buy" rating. Janney does say that the company has a "multitude" of problems, but thinks the stock is a good value following a 75 percent decline, with Mark Speese returning as CEO.

Cedar Fair — Goldman Sachs initiated coverage on the amusement park operator with a "buy" rating, while calling rival SeaWorld a "sell." Goldman said Cedar Fair has multiple growth drivers that are not reflected in current consensus estimates.

NetApp — JMP Securities upgraded the chip maker to "market perform" from "market underperform," saying the move toward all-flash memory devices will continue to drive sales growth.