Hi guys,
Yeah, windmilling is very common for all big high-bypass engines whilst shut-down on the ground (and, come to think of it, inflt too!).
Anyway, no prolems except for engine start in windy conditions when the wind is from the rear quarter. Sometimes, the backwards windmilling fan will be very slow to start turning forwards, and can cause abnormally high EGT start peaks, sometimes TOO high, and cause precautionary aborted starts.
I remember that when engine starting the RAAF Mirages (a few years ago now!), if the wind was from the rear and windmilling the engine the wrong way, we couldn't start at all. So they incorporated small 'blowers' on ground crew backpacks to blow air down the intake at initiation of start, to have the engine turning the correct way, and it started OK.
Getting back to the big engines, if you were close enough to hear, the fan blades are also moving in their mounts with each rotation, causing a quite loud 'clanking' noise, also quite normal to those that are around airplanes all the time, but a concern for remotely loaded pax, from the bus, when they walk past Nos.1&2 engines and up the forward steps, I hear the FAs calm their concerns several times each time we are in that situation.
Cheers