by far, the biggest culprit for belt noises is the tensioner..
they stick
loose tension
walk apart
seize pulley bearings
make all kinds of rude & disgusting noises
I keep about 10 or so different numbers in stock at the shop...
the "problem" is not limited to 7.3's, or even Fords for that matter..
GM 6.0 gassers have problems with the AC tensioner
the 3.1 & 3.4 Chevy motor like to walk theirs apart,
and the 3.8 Buick engine has a nasty habit of siezing up the pulley...
Chrysler has had ongoing problems with the tensioner on 3.3's
Ford 3.0's & 3.8's are notorious for just blowing them apart like the V6 Chebby's..