A loose flywheel quiets down when an automatic trans is pulled into gear, or a Fred Flintstone manual transmission is loaded down by slipping the clutch a little. The noise goes away, or at least changes pitch, when the bolts have a little load on them.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!