Couple of thoughts...
1. The clutches should last about 150,000 miles, depending on usage. Ford published it somewhere, but you'd have to do a little searching. It's based on a statiscal approach, something like Ford expects at least 70% of will make at least that many miles (which accounts for the track users vs the grannies, etc...) Don't quote me on the percentage though...
2. A few folks threads and various searches have found the grinding/chattering is due to an oil seal leaking the tranny fluid (yes, it has tranny fluid) onto the clutches. Rumor is if the fluid leaks enough to show up outside the bellhousing, it's an easy warranty claim.
2012 Se Ingot Silver 5-Door w/ 201A & Se Sport Package
2001 Silverado 1500 RCLB 4x4 4.8L 5-Speed