It would help to have a model number to diagnose this. Many whirlpool dryers have the drum suspended on a spindle that is in the back. The bearings on that spindle can fail causing the drum to squeal and eventually seize. Since you have already taken it apart once, you can confirm this. Post back the model number.
DanO our resident appliance expert may check in and will have suggestions, IF you can reply with the model #