Our 2001 Acura MDX is having a mystery vibration that starts at 55-60 MPH. It doesn’t always vibrate at this speed, but it does a lot of the time. We replaced the tires (they didn’t have uneven wear or anything), and it didn’t help, and the only real clue we have is when we jacked it up to look underneath this piece fell out. We don’t know what it came from, it looks like a piece of some sort of machine foot, but when I look at pictures of the motor mounts it doesn’t look like anything on there. I know it’s a long shot, but does anyone have any ideas what it might be from? Or any ideas about the vibration/shaking?