My Storm came with only grease on the diffs. I have sinced added diff oil and it made a big difference on the track. When my buggy is on the starter box, and I spin any wheel, the only sound I hear is the sound coming from the pinion/spur. That's it. Without taking a few things apart it's hard to say where your grinding is coming from. Could be the diffs, and your turning problem might be a hint that there is a diff problem, could be dirty bearings in the wheels. If you can hear this grinding while you're running, either you have very good hearing, or the grinding is severe. Take the time and check it out now before what might be just a dirty bearing or worn spider gear, turns into something bigger.