On a road trip yesterday noticed a new noise. Initially thought it was road related, almost like the indentions on side of road to prevent veering off, but not as dramatic, but saw that the road is smooth. Once we determined it was an issue with the truck, we noticed that it would quit when you take foot off accelerator. No other issues such as clanking when shifting into gear. In fact, I can manually shift to another gear and the noise doesnt change. Any ideas on where to start? Thanks!