There is also a possibility that the vibration you felt was merely the wheels spinning as they are retracted into the wheelwells.
If the tyres are unevenly worn, as most are (being retreads) then the wheels will be out of balance (like on a car) and a vibration will be felt throughout the plane.
We often feel it on the B738, and I do recall feeling it on the B744, but those are from the nosewheel.
Hope that explanation puts your mind at ease.