This is equipment of Steel Industry from Bar Rod Mill unit. Equipment is Mill Stand, Which is having reducer gear. The Input shaft have 24teeth and mating gear has 63teeth. Intermediate having 19,66 teeth and output shaft having 31,31teeth. I didnt have any problem with vibration whenever the higher dia bar is rolled vibration will be 4.0mm/sec peak and during lesser dia bar rolled it will 2.5mm/sec peak. The spectrum is showing a high amplitude dominant peak of 73.1orders of input speed at all bearing points of gearbox.. Neither it matches any of the bearing fault frequencies nor gearmeshing.. Input speed is 1033rpm. What may be the reason?? I checked the bearing fault of stand bearings even it doesnt matched..