MCM5595

okay so when starting my truck it makes a weird knocking/ spinning noise this doesnt go away after it warms up... it only happens at low RPMS or during complete stops.. and it only happens for a couple of seconds, it sounds like somethings loose i dont wanna go underneath and take a look as it is quite cold ( and it does it in the hot weather too) I dont mind the sound i think it makes the truck sound a little more beefy but just wanna know if i need to repair it.