First check the drum itself, to make sure nothing is loose inside (maybe some coins). If there is nothing in the drum, then something has probably gotten in the blower housing and the blower wheel is moving it around. The blower wheel turns whenever the drum is rotated (see picture). You can check this by moving the dryer out, disconnecting the power cord and taking the vent hose loose from the dryer. You can now reach inside the vent and turn the wheel and see if it's hitting something. Be very careful, making this check. It's possible it could be something sharp and might cut you. If you do not feel confident repairing this problem yourself, then you can have it repaired at your home by a Sears technician. Here is a link for the website:
Sears Home Services
. If you need more assistance, please resubmit your question, with additional details.