Dona: Are you moving into my home? Just kidding, but I also live in a 1996 single-wide Fleetwood, 16X80 with a peaked metal roof. And yes, it is "normal" listening to the roof flex and rumble on windy days. Basically, the sheet metal was placed over the trusses on the roof, and only fastened along the sides where the roof material is folded over the outside walls. Where the roof is bending and flexing is over the trusses. Don't go up there on a windy day or you'll get seasick watching it!
It doesn't look very sturdy, but I have lived in this particular home for over 10 years now and have only experienced one roof leak, and the roof has withstood gusts of wind that exceeded 70 mph!