Well I downloaded the recommended manual and studied it to prepare to take apart my dryer. I have fixed a washer twice, but this seems much more daunting to me. I guess I have to take the drum out to look at the rollers.
Also, I checked the exhaust vent that was formerly on the dryer and it is plastic. Not sure how long my mom operated the dryer with the plastic vent. I am pretty sure that was how it was installed. If the dryer was operated with the plastic vent hose, is it still worth trying to fix the knocking, or am I going to get into bigger issues with this machine. I just don't see myself repairing heat elements etc.