a magnetic ballast will produce a magnetic waves and sometimes if the housing is close to the ballast, it will rattle......what u can do is check ur fixture if there are any loose materials that can cause the rattling sound.
as for capacitor, its not really necessary as it is only use if u are running alots ( i meant a lots ) of lights...etc in a bulding. for that case, that it will save electricity. if not, it does not matters.
if u look at all e german fixture, they also do not include any capacitor....
cheers