We have a vibration problem of an ID fan of 75 KW motor driven. Spectrum having dominant 1x rpm initially with overall vibration 6.0 mm/s and also phase shift of 65 degrees between H and V at FDE. From past week there is sudden increase in 2x which is as much as 1x rpm in the FDEH spectra. Alignment readings are found ok and so phase. Plummer block bolts were also tight and good.Can the prevailing unbalance can cause an increase in 2x rpm? What are your thoughts?