my saturn makes a loud grinding noise also mileage is is kilometers

when starting my 03 saturn in the morning not all the time but sometimes it will make a loud grinding noise this problem also occurs sometimes when driving and i have also heard in neutral when stepping on the gas. cannot figure this out for the life of me need someones help it has been making this noise for about 4 months once again it is a very loud grinding noise been to many repair shops and they cannot figure it out