I put a Good-Year Gator Back on my Zetec and it's very quiet. Your tensioner is likley worn so the belt is loose.
Insure all the pulleys are clean-no slipping/belt squeal.
Also make sure the pulleys line up accross center.

95 Contour GL. Bought new. BAT Sway Bars/Pioneer CD/Koni Rear Struts/Mobil Fluids. Looking for 15" alloy rims-PM me. 180,500km's so far.