We have the same engine as a F100, and our manual suggests, for taxiing in icing conditions, to periodically run the fan speed up to 60%, to avoid ice accumulation behind fan blades...
It has been my assumption that the same procedure applies if a fan that's icing up starts to vibrate... if a short run-up of power gets rid of the vibration, fine, otherwise investigate further..
Have I been to cavalier in my attitude to fan-blade icing?