The S&P 500 was down 0.3% in midday trading to 2,024.03.
The Dow Jones Industrial Average was up 0.1% to 17,234.98.
The Nasdaq was down 0.6% to 4,850.92.
The yield on a 10-year Treasury bond was down 2.5% to 2.02%.
The price of gold was down 0.9% to $1,166.
Irvine-based Western Digital Corp. was down 3.8% to $72 and a $16.7 billion market cap. The storage products maker said it would buy a competitor, Milpitas-based SanDisk Corp., for about $19 billion.
Lake Forest-based Del Taco Restaurants Inc. was down 4.3% to $13.13 and a $510 million market cap. The fast food chain was lower on sector weakness related to results at Denver-based Chipotle Mexican Grill Inc.