Originally Posted by djeucalyptus

if tightening the cranks bolts doesn't help, I'd pull your cranks and check the squareness of the taper, as well as the squareness of the bb spindle.

If tightening doesn't help and you're sure the sound isn't coming from any other parts, it's probably only very slightly out of whack. you won't do any catastrophic damage, but it will probably slowly wear away at the cranks/bb and may eventually lead to having to replace some parts. Just keep everything snugged up as much as possible.