What stocks Warren Buffett is buying is a closely followed story by many investors. However, since he's known as a buy-and-hold investor, it's less common to hear someone ask "What is Buffett selling?" However, Buffett does unload stocks from time to time. While there's no way to know for sure which of Berkshire-Hathaway's (NYSE:BRK.A)(NYSE:BRK.B) stocks will be next to go, here are three that our contributors feel could be on the chopping block.

Sean Williams: To be clear, Warren Buffett is a buy-and-hold investor that isn't known for regularly parting ways with his holdings; thus anything we say is nothing more than speculation at this point. But if my arm were twisted, I could see the Oracle of Omaha and his team parting ways with French drugmaker Sanofi (NASDAQ:SNY). As of the latest 13-F filing with the Securities and Exchange Commission, Buffett's Berkshire Hathaway owned 3,905,875 shares of Sanofi, worth $173 million as of April 25.

Why Sanofi? I see two reasons that stand out. First, Buffett himself has always had an aversion to babysitting stocks he owns. He wants to buy businesses that he could sock away for 10 years and not worry about. With drug developers like Sanofi, you have to, with some regularity, keep up with clinical trial data to understand what new therapies could be coming to market, as well as what developing products missed the mark. Buffett simply doesn't have the patience or resolve to do this, which is why he's tended to avoid pharmaceutical companies.

The bigger issue for Sanofi might be that its core drugs are all hitting the end of their patent-protected life cycle. Within the U.S., Lantus and Lovenox have come off patent, and Plavix is facing pressure in other parts of the world. Combined, these three medicines equated to a third of Sanofi's 2015 pharmaceutical sales, and all three fell on a year-over-year constant currency basis. Sanofi does have its fingers in multiple collaborations, but even those don't always work out (ahem, $325 million lost partnering with MannKind's Afrezza).

I believe it's possible that Buffett might look at Sanofi's rather tepid growth prospects and go in search of better places to park his money.

Matt Frankel: I wouldn't be surprised to see Berkshire Hathaway continue to unload its AT&T (NYSE:T) stake. My main reasoning here is that AT&T isn't a Buffett stock -- nor was it a pick of anyone else at Berkshire. The shares were acquired when Buffett stock DirecTV was bought out by AT&T in a cash-and-stock deal.

Berkshire had its reasons to like DirecTV when it started building a stake in 2011. After all, there was only one real competitor (DISH Network) in the satellite TV space, and DirecTV was by far the larger of the two and had significantly better margins. Plus, DirecTV had been building a strong and growing presence in the Latin American markets, where satellite TV was still a growing industry.

However, AT&T is a different kind of company entirely, and one that Berkshire didn't choose to build a stake in. Besides, once the buyout took place, Berkshire was sitting on a pretty handsome profit from the DirecTV investment, so some profit-taking makes sense. In fact, Berkshire received 59.32 million shares of AT&T during the third quarter of 2015, and unloaded 12.7 million of them in the fourth quarter. And I wouldn't be surprised to see further selling in 2016.

Brian Feroldi: Warren Buffett is famous for buying and holding companies for the ultra-long term, but when I scour over his investment portfolio, I can't hep thinking he would happily unload some of his General Motors (NYSE:GM) shares if the market offered him a modestly better price.

Buffett owns about 50 million shares of General Motors, which at current prices is worth about $1.6 billion, so he clearly likes something about the auto giant right now.

That appears to be a timely buy, as the company is really firing on all cylinders right now. It just reported a blowout quarter: Revenue grew by 4.5%, and the company greatly expanded margins, which caused net income to more than double, blowing past Wall Street's estimates. GM also boasts a strong balance sheet, with more than $30 billion in total liquidity versus only $10.8 billion in long-term debt. The company is buying back gobs of its own shares, and it pays out a big dividend.

Yet despite all that, the market doesn't really seem to care. Shares have barely budged since the company's IPO in 2010, and they're fetching about five times earnings. What gives?

My hunch is that the market is worried that the company is only doing well now because of low oil prices and that its fate will turn when oil rebounds. In addition, I believe some investors are worried that ride-sharing services such as Zipcar, Uber, and Lyft could put a serious dent in the long-term demand for cars, since they allow consumers to access all of the benefits of owning a car at a far lower cost and with none of the associated hassles.That's especially true when you consider that the world's population continues to flock toward city living, where the upside to using ride-sharing services is greatest.

I'm sure that Buffett is aware of the long-term threats to the auto manufacturers, but he just sees too much value in General Motors stock to pass it up. That's why I think he could be willing to unload his shares if the price were to rise.