I've noticed a slight "bump" while driving my wrangler around. It's most noticeable between 10-20mph, but you can tell it's there at any speed. It feels like I'm running over something about the size of a marble or small rock with every rotation of the tire. There is no noise, I've checked the tread (nothing stuck in it or any bulges that I can see), there's no shake or shimmy to my steering wheel, and it feels like it's coming from the driver's side rear tire. Not sure what could cause this. I'm getting ready for a road trip this weekend, so I'll probably end up taking it to a tire shop just to be safe. Just curious if anybody had any ideas as to what is causing this.