The Dow Jones Industrial Average (INDEX: ^DJI) managed to end the day in the green after dropping as many as 109 points during mid-afternoon trading. Other than a brief moment after 10 a.m. ET, the Dow was lower until just before the closing bell. Seventeen of the 30 Dow components ended the day in the red. Caterpillar (NYSE: CAT) was the only Dow stock that released earnings today, but a few of last week's announcements were still affecting the market today, as did nervous investors waiting for earnings coming this week.

Three stocks that moved lower before their earnings later in the week were 3M (NYSE: MMM), Boeing (NYSE: BA), and AT&T (NYSE: T).

So why are they down?
3M is set to announce third-quarter earnings tomorrow morning. The company ended today's trading session down 0.44%. Investors may be getting ahead of themselves and selling on fears that the company will miss analysts' estimates. The pros are expecting earnings of $1.66 per share and revenue of $7.85 billion for the quarter. These are both higher than last year's actual numbers by 9.2% and 4.2%, respectively. The analysts are expecting strong growth, and with the numbers we have seen from other companies this quarter, those numbers are going to be hard to match.

Airplane manufacturer Boeing saw its shares fall by 0.42% today. The company is set to announce its earnings on Wednesday, but tomorrow it is set to increase its production line capacity by nearly 20%. Currently the company builds seven planes per month, and on Tuesday that number will increase to 8.3. The increase is an attempt to reduce its backlog of more than 4,000 planes, as well as increasing revenue and profits. This should be a good thing for the stock price, but tomorrow Boeing's rival Airbus is planning on doing the same thing. Lastly, some investors could be worried that increased production rates may increase defects and delays in actual delivery. Currently there are about 40 planes that still need work after leaving a temporary surge line in one factory. Investors can only hope this is an issue with just that one factory.

AT&T also saw shares tumble today, by 0.17%. The telecom giant is expected to announce earnings on Wednesday and may be declining today as a result of Verizon's (NYSE: VZ) earnings announcement. Verizon didn't have a huge number of iPhone 5s sold in the third quarter and thus didn't take the huge subsidy right off, but AT&T may be a different story. The subsidy the service providers pay to Apple (Nasdaq: AAPL) can have a huge impact on the company's earnings, which then hurts the share price in the short term.