The predominant frequency is the basket speed at 898 cpm, what does the waveform (time signal) looks like?, I am leaning to say you have an imbalance problem on the basket and it is shaking the motor as well. The waveform should give an indication also if it is an imbalance problem.
If this just showed up on the basket and has been operating find I would suspect it is a case of uneven loading creating the imbalance problem, sometimes cause by the consistency of the product.
If it has been there from day one, then most likely it is a imbalance on the basket itself especially if readings taken were there before any product pass thru it.
I am not sure if you can zip the file when you take readings on OFF Route equipment, but if you can please post it, this makes a good case history.