I would pull the whole fan/motor assembly out and put 115 volts to it with a cheater cord, you might have a unbalanced fan blade or bad rubber end bell supports. If there is play in the motor shaft, or it screaches, replace the motor.

The freezer evap fan motor is vibrating excessively causing a continuous loud noise when running. I tightened all housing screws and the back panel on the inside of the freezer and the plastic guide for the fan output. This only helped a little. Could the bearings on the fan motor be going. It has been getting worse over the past few weeks but now it is very bad that it is easily heared on the second floor of the house at the opposite end. Any advise is appreciated. Thank you.