Welcome to the great world of sensing.
Hearing things while it couldn't be possible because there's nobody there could be caused by everything. Dimensional drift, ghost, whatever. Feeling presences could be anything too. Somebody/something projecting, an astral creature like a 'demon', etc. No need to worry. Just get used to it, there isn't really anything you can do against it.
every now and then when im sitting donw or walking or whatever i got this like sudden presence near me i dont know how to describe the feeling its just like a wall of air just goes right by me or like sometime i can hear (this i cant explain) some one walk on the carpet coming near me or walking right past me or when im in my room just about to go to sleep i feel somethin come in my room and stay there could it be someone projecting or what i dont know........