I traded my Wrangler Unlimited Rubicon in for a Trail last Friday. I noticed a thump-thump sound at slower speeds right away and can also feel it in the brake pedal. Took it for a test drive with service mgr yesterday. He acknowledged the noise and suspected a bad tire (flat spot). I left it with them today. They replaced a tire or two and now suspect bad backlash in the front diff. A Toyota field tech is now involved. Right now the plan is to replace front diff and axle shafts. They may not get the parts until early next week. I'm driving a loaner Camry now....