You may have a grain of sand or something in the impeller shaft area. Also, check the shaft for any damage to the little plastic end caps. I had one with a small crack in the shaft cap and it sounded like I poured a handfull of sand into it.
If you can't see and damage, try swapping the impellers. If the sound transfers then you just need to replace the damaged impeller.
If you can't see and damage, try swapping the impellers. If the sound transfers then you just need to replace the damaged impeller.
