The nice little buzz circulating around the White Sox’ future rotation this week lost some of its hum when left-hander Carlos Rodon was scratched just moments before his scheduled start Thursday against the Indians. Rodon, with the likely inside track to become the Opening Day starter in 2018, had gone to the bullpen to warm up but cut his pregame routine short and was scratched because of shoulder stiffness. It was a concerning development, considering Rodon missed a significant portion of spring training and almost all of the first three months of the season with bursitis in his upper biceps, which essentially is a shoulder problem. Buzz off. “Yeah, just didn’t feel right warming up,’’ Rodon said after the Indians trounced the Sox 11-2 without him. “I can’t really put a finger on it. Just a day you don’t feel right, and you don’t want to . . . compete when you’re not at your best, you know. Didn’t feel right.’’ Rodon will have an MRI exam Friday. Right-hander Mike Pelfrey (3-11, 5.51 ERA) started in Rodon’s place against Indians right-hander Corey Kluber, perhaps the top Cy Young contender, who would improve to 15-4 and keep his ERA at 2.56 while helping the streaking Indians roll to a franchise-record 15th win in a row.