it could be nothing but why take a chance. i'm a worry wort about these things though. i don't mean to make you nervous, just get it checked so you have peice of mind. i hope it turns out to be fine, i have heard that some ballasts do humm louder than others. suprisingly, i only used 1 ballast my whole life(repaired several times at the hydroshop) and i could just have just got lucky and had a really silent one so that is why the buzz you talk of made me nervous. good luck.