Just bought 2012 800 etec renegade x. This is my first xp chasis. The sled only has 2000 miles on it. And when I have the ass end lifted in the air and give it some throttle to get the track moving, it makes a bad grinding noise. My hunch is driver bearings or chain case. I checked all the bogie wheels and they all seemed to spin freely. I haven't had much time to really look into it. Just wanted someone else's opinion to see what you might think it is.