Pontiac Firebird makes noise over all bumps

Hi, I have a 2002 Pontiac Firebird formula 32,000 miles with a 5.7 liter V-8. Every time im driving my car over a bumpy road or any bump at all it makes a noise from underneath the car that makes a clanking sound like something is loose and hitting. I've watched my dad go over a bump to see if it was the exhaust but i heard the noise but the muffleres never moved. We've taken the car to a dealer to see if they could fix it but they've checked the car and said nothing was wrong with it and they said these cars make noise all the time. I'm willing to live with it but every time i go over a bumpy road i feel like im hurting the car. If you have any suggestions on what it might be please let me know what i could do about it. I love this car and hope to keep for as long as possible. Thanks alot.