humming noise from back of car

my car is making a loud humming noise after it has been running a while it is coming from the back of the car does anyone know what this may be please tell me?

thank you

Tell us more is it only while moving ? does it go away while rolling with engine off?
Poss items to look at .Wheel bearing -tire- exhaust-
Tell us more then we can talk more
Dave

Probably the fuel pump if it stops when you shut the motor off.

I agree with Jeff, I would suspect a fuel pump, given the limited info given on the original post.