We can call a person Noble ( not the medieval nobles) when he is full of honesty,( it should be well known) gentle in behavior, full of ethics & etiquette . That person can be called noble. Money or richness should not be counted in it.
Your question has many parts . Noble act can be done by any one , if any one does any selfless job for the betterment of many it can be called noble act .
Noble profession usually those who do humanistic work . Such as doctors , teachers , nurses.
( though many criticize these professions as many doctors charges very high ) .Still these people handle you , when you utmost need them.
According to me many people now do may environmental work for the protection of wild life , conservation etc. , they are also do very noble act.
In medieval period rich people were considered as noble or together nobility .But with educated mind , & scientific temper , rationalism in our head ,we are not ready to accept such thing any more .Yet if we see too much rich people ( with out knowing their character) we look at them in awe , we make mistake by thinking them as nobility.
