yeah, they will definitely howl a bit if you don't get that pinion depth set properly and the preload on the crushsleeve correct. i would bet its not in pattern.
either that or even from crap gears, though if yours are ford racing i doubt that.
eyeballing it, unless you've done hundreds of differentials, is a terrible idea. Ive seen some people who work at trans shops working on diffs all day long eyeball em perfect, but for me i would check everything with the proper dial indicators and things.
mine dose the same sort of noise under SUPER light throttle because i reused the old 3L27s and just tossed some new bearings/races in with the old shims, and resealed it a new pinion nut and crushsleeve.
pretty sure the 180k on the gears with worn bearings cut the pattern a bit wonky, new bearings and stuff put it all back to spec and now its not meshed perfect from the wear.
the gear oil was horrible, probably not the original stuff, but close.
i plan on some 3.73's eventually anyway, when i have the extra cash for a good set.