Bottom Brackets are funky. My teenage son's Rockhopper's BB is crap. It's a 10-15 dollar one and he's broken his 2-3 times last year and and once part of this year. Then the left crank fell off because the BB had been stripped. The whole crankset needs replaced. Makes me mad as I spent a LOT of money on this bike because I know he loves riding and realizing it's a "cheap" bike in the cycling world. And no, like you, he's not abusing the bike.

Kind of sucks you can't just get a better bottom bracket w/o having to buy an entire new crankset. I'd probably just keep replacing it for now. My son's Rockhopper creaked/popped as well.