Back tire rattling noise when I hit a bump but stops when I press the brakes. ?

It rattles constantly and when I got a bump it sounds the worst. I took it to two shops and they inspected the brakes and neither of them found anything out of the ordinary. Well I was looking around myself and found a loose metal cover underneath the car so I took it off. Still continuing to rattle. So I kicked the tire and that’s for sure the issue. Something with the tire. Every time the tire has a little vibration, it rattles like something small and metal is broken or loose. Any ideas what it could be specifically?