The timing belt on my Zetec will usually hit the top cover when I first start the engine (cold). This I'm told is normal, but should go away once the engine has warmed up. I've read that rubber belts like this one actually shrink slightly when warm rather than expand so they tighten up after they've run awhile.
The belt on my daughter's Contour was replaced at around 88,000 along with the tensioner. It was making a considerable racket like what you describe. Taking off the top cover the belt had started to shred itself.
Ford dealers I've talked to recommend the belt be changed at 60,000 miles. The owner's and factory shop manual have no replacement interval listed at all. Someone here mentioned that 120,000 is a reasonable interval. Mine just turned 98,000 and seems fine. I'm going to put off the $250 expense as long as I can.

- Jim Our yardbirds: Belvedere, our '96 Jeep Cherokee, 4.0L ATX, 85,000 and going strong Spencer, our '03 Chrysler PT Crusier, 2.4L ATX, 28,000 and just getting started