So, my truck has started having a weird grinding issue coming from somewhere in the back half of the vehicle. It only happens when going up hill and having apply the go pedal to overcome my own momentum. I have yet to hear/feel this going on flat road or down hill, and it happens 98% of the time on the highway. It does not do this around town (50mph and under). I replaced a wheel bearing last year and it is not making the same noise it was when I figured that needed to be replaced. It is extremely hard to troubleshoot since I can only do reproduce the sound on certain stretches of road. Any ideas?