Stick a large screw driver on the motor in the area of the bearings and on the pump housing ... stick the handle to your ear (notice I said to your ear ... not IN your ear) Listen. Often you can determine the source of the noise in this manner.

My money is on the impeller. You will need to replace the seals when you disassemble the pump motor from the pump housing. I found a dime in the impeller recently ...it made a racket until the impeller wore down in that area.