Guessing you have an auto? If so, first check the fluid level.
http://www.omegaowners.com/forum/index.php?topic=90508.0If that does not remedy the matter then if you want to use the following, please take great care and find a VERY suitable piece of private roadway and check that it is safe to continue.
Get the car upto speed (30-ish so that the noise is apparent) then slip it into neutral with engine still running. See if noise abates. If it does then looks like a potential gearbox issue but not conclusive.
If not, whilst doing 30-ish, switch off the engine BUT ONLY BACK ONE CLICK ON THE KEY THEN IMMEDIATELY FORWARD AGAIN ONE CLICK TO BRING ON THE IGNITION LIGHTS AGAIN. You are now coasting in neutral. If you switch all the way off as you would so as to remove the key then you lock the steering and thats not clever if you are doing 30-ish on the public highway with other vehicles, pedestrians and hard jaggy things that you might crash into.
If the whine goes away it is engine related and worthy of further inspection.
If the whine is still present (and doing 30-ish in neutral) then its gearbox/transmission/wheel bearings. No short fix solution but you are tying down the area of investigation.