[nhramnl]

"Almost new" means they've been set up before and ran for some period of time with that relationship between the ring gear and pinion. They "got used to each other" during that time, and unless you can re-set them to exactly that relationship (and you can't), they will howl. Also, drag race gearsets tend to be set-up for deeper tooth engagement (for durability) and that seldom means a perfect, quiet contact pattern.