High vibration on centrifugal pump

Dear expertise, 

 

I need your suggestion, 

 

I have a case and need your advise.  I have centrifugal pump 2975 rpm,  520 kW. In april 2017, i have a dominant spectrum in 1x and 3x,  1x = 0.673 mm/s,  3x = 1.162 mm/s.  But suddenly when I throttled the valve on 10% opened,  the spectrum becomes 1x = 0.334 and 3x = 5.116 mm/s. Found harmonic 1x motor speed. 

Firstly I thought that is the effect from cavitation.  But i didn't see any raised floor on high frequency.

 

Note : this pump using sleeve bearing on DE and NDE. EC00003

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