Front diff. failure at 20,000 miles

I took my truck in this morning to have the amplifier replaced. The roads were iced up, so I put it in 4-wheel drive. It engaged fine but it sounded like I had an extra muffler up front and ther was quite a bit of vibration that would come and go depending on how much gas I gave it. More gas=more noise and vibration. The mechanic looked into it and said there was a huge amount of backlash in the front diff. I've read about alot of rear diff. failures but not so much about the front. I've only engaged 4 wheel drive maybe 6 times, driven maybe 200 miles with it engaged. Any other Titans out there with this problem? What year is your truck and how many miles before the failure?