I haven't heard the terminology "Omega 3" before, so I could be way off topic. Omega is sometimes used to indicate rotor speed and a 3 bladed rotor will have a vibration at 3 times the rotor speed, so I'm guessing Omega 3 is this. Terminology I've used is "3 per" which is short for "3 per revolution" or in general, N-per (N is the number of blades).
These N-per vibrations occur due to blade interference with something like the fuselage or the tail rotor. Because each blade is supposed to be doing the same thing at the same azimuthal position, the vibration occurs for each blade giving a "beat" every time a blade passes through the area where the interference occurs. Hence you get N beats per revolution at a frequency of Omega x 3. That might be what you're talking about.
1-per vibrations are related to the track and balance of the main rotor and can normally be reduced whereas N-per vibrations aren't directly affected by t&b.
Am I close?
Matthew.