i just put new tires and some slightly used bridgestone heavy duty tubes that i got from my neighbor on my husky the other day. i set the pressure on the front to 13 psi and the rear 12 psi. i went out for a 15 mile ride in the rocks/mud and when i got back, i put the bike on the bike stand. upon me turning the rear tire, i heard something rolling around inside the tire/tube. i checked the tire pressure and thats about the same, maybe a pound lighter and the bead is set around the tire. so at first i thought that i must have gotten some dirt/rocks inside the tire from the ride but the more i turned the tire, the more it sounded like whatever was in there, was coming from the inside of the tube. so a few questions...first, what is inside the tube that sound like balls or marbles rolling around? second, should i be concerned or should i change out the tube? thanks.