I am seeking advice on vibration. We have a vertical spindle pump motor 1385kW 3300 volt six pole squirrel cage constuction DOL(one of three). On test in the repair shop the balance is fine(no load)Top bearing 0.9mm/sec, bottom bearing 3.4mm/sec (different power supply). On it's pedistal, coupled or uncoupled from the pump when under power there is a serious low frequency vibration which is visable and transmitted to adjacent similar pumps. At the very instant of being switched off the vibration stops. When moving this motor onto other pumps/pedistals the vibration goes with it. The power supply has some variable components of unbalance from zero to 10% but has no affect on any other similar plant. Any ideas?