Keith Monnin, CEO of Bernardi Auto Group, looks over a dealership in Framingham, MA. Suzanne Kreiter | The Boston Globe | Getty Images

A growing number of auto dealers around the country is seeing a noticeable drop in retail sales and customer traffic in showrooms, raising the possibility that a long-anticipated slowdown in auto sales has arrived. "We are definitely seeing business pull back," said Scott Adams, the owner of a Toyota dealership in Lee's Summit, Missouri, just outside Kansas City. "September was off some, but this month our car sales are down 12 percent and our truck sales are down 23 percent."

Other dealers tell CNBC they saw a significant drop in sales last weekend. One dealer in metro Tampa Bay, Florida, who asked not to be identified, said sales this month are down 13 percent. "Customer traffic has moderated," said Mark Scarpelli, president of Raymond Chevrolet and Kia in Antioch, Illinois. Scarpelli said sales at his dealership are "keeping pace" with last October, but he has seen customers taking longer before buying a new car or truck. "There is a little bit more of a pause because of the higher interest rates," he said. Auto loan interest rates have moved steadily higher as the Federal Reserve has raised rates this year. In the second quarter of this year, the average new vehicle interest rate was 5.76 percent, up from 5.2 percent at the same time in 2017, according to Experian, which tracks millions of auto loans.