Fan blade icing, possible on the ground.
Freezing fog ice tends to be migrate towards the tip and /or be shed tangentially where ice from the leading edge of a preceding blade strikes the rear of a following blade directly or after ricocheting from the fan casing.
Some engines have a procedure for on-ground ice shedding requiring a moderate increase in fan speed at set intervals; if not the problem may be encountered during the high power take off settings.
The crew may detect a fan buzz when on the ground.
Any F100 pilots for comment.