Avoid sleeved shafts. The shaft was weakened to install the sleeve. If you use a corrosion resistant shaft with a non fretting, balanced O-Ring mechanical seal, there is no need for a shaft sleeve. Check for excessive pipe strain. Make sure the shaft is not bent.
Most people have no luck in trying to straighten a bent or warped shaft.
Check that the rotating parts have been dynamically balanced. Make sure the bearings are in good shape. Check for vibration. There are many sources. Different types of cavitation.