Bearings usually start out making a slight whining sound. As they get drier, they get louder and the pitch changes from high to a lower growling sound. This is my description but not necessarilly a good one. If your motor is getting louder, its the bearings.
I find that the average life of a ball bearing in a pump motor left out in the weather here in Florida is 7 years. We can usually rebuild that motor with new bearings etc. and it will go another 7. That is if it's a good brand motor. Cheap motors don't last anywhere near the first seven.
bob...