Unhook the belt from the motor and turn the drum by hand with the machine loaded. If there is a bearing problem you will hear and feel it. Sometimes the noise is just at the front where the felt or nylon support has worn away. This can be fixed by replacing them. If the noise comes from the back then it is probably the bearings. No abnormal noise or movement means the drum is probably ok. It could be the belt tensioner dry and squeaking.
It may be worth fitting a new belt if you are going to do the bearings, but if the old one is in good condition it is not necessary.
Colin
February 2008