I've got a problem with the evaporator fan in the freezer. It makes a high pitched whining sound that is very loud and annoying (seems to come on more during the evening). I've replaced the fan itself, and have access to the motor. I have no problem ordering a new motor from this site, but how can I be sure that the motor is the problem? It seems to run fine for awhile at normal speed, but then it slows down a little and starts emitting the noise. What can I do to make sure that I correctly deal with the problem? Thanks.