2012 Ninja 250R (EX250JB)
Mid RPM (most notable): engine harmonic.

Anyone familiar with a twin engine boat or plane will know the harmonic vibration I’m referring to when the engines are not in sync. My 250 has an eerily similar harmonic: low frequency at lower rpm (5000; waaaawaaaawaaaa) with a steadily increasing frequency at steadily increasing rpms (9000; wawawawa).

Any suggestions what might be causing this and where to begin adjustments?