I have a strange engine sound. 2011 Prius with 114k. Unknown maintenance history. Being sold by Carmax. When the engine kicks on there is a scraping sound like something is dragging even when the car is not moving. Happens when I drive slowly up to about 40 or 50 then don’t hear it anymore. If I accelerate under electric power only there is no sound. As soon as the engine kicks on there it is. The sound doesn’t change with speed. Sounds the same sitting still as it does going 50. Any ideas?