C180 Kompressor 2004. Driving this morning when dash flashs red warning Battery/alt visit workshop. and noise from alt under bonnet this happened on and off for 1/2 an hour then cleared itself before I had chance to visit workshop? any ideas? would you see if it happens again as there is no point in taking it in when not doing it! Could it be the pully on the alt and is it replacable without renewing the alt?