heavy looking object; stationary; hovering and very loud

This object was an irregular shaped  object that looked very heavy and machine-like.   It was dark in color - like a dark grey and was very loud.  So loud that it caught my attention from inside my apartment on the 15th floor of a high rise.  
It  stayed in one place for the entire time I watched it (about 30 minutes) and was very close to the building.  I was amazed that other people did not hear the noise and come out to see what it was.   
I was determined to watch it  and would take my eyes off of it.  I got tired, and after a while I grabbed a pillow to lie on my floor and watch it to see how it would move and what it would do.  
I fell asleep and it was  gone  when I awakened.  
It was one of the two strangest  things  I had ever seen up to that time because it appeared to be too heavy to be just hovering (actually, comopletely still) in the air, so close to me,  making so much noise.   
The shape was not smooth, but sort of  oval-round.    
I have  never heard of any object like this and wonder if any other person out there has  seen anything similar.
Witness indicates that date is approximate.  PD