Last month as I was driving to work I heard what can be described as a "metal spring vibrating in a glass jar" sound. It's a higher pitched oscillating noise and only happens in 2nd/3rd gear - maybe between 25 and 40mph - when going up a slight incline. The sound has been getting louder and more frequent. If I let off the gas or gun it, the noise goes away. I haven't gotten under the Jeep yet to look for loose parts but has anyone else experienced this? If so, did you narrow down where the vibration came from? It can be heard both outside and inside the Jeep.