15 year old Kinetico 30 getting loud ...

I have a Kinetico K-30 water softener that is about 15 years old, and lately it makes a loud humm when water is running in the house. You can feel the head of the unit vibrating when it hums, like there is a loose washer or something. Is there regular maintenance that should be done on this unit? Any idea of what it could be? Also, I have the original resin beads - is it about time that the resin should be changed as well? The unit has been great - no problems up until now. Am on city water. Thanks much .... -dog

Found that the bypass valve (to bypass the softener) was stuck open - haven't closed it in years. I lubricated it and worked it free so it opens and closes smoothly, and the loud humm is gone now. Maybe this freed up a vibrating washer?