low hum when in 4x4
i have a 09 f350. this is my first 4x4 so bare with me. i noticed the other day when i put my truck in 4wd because of snowy conditions i could hear a kinda faint hum at low speeds. tonight i tried it again since we had a bit of a snow storm and i confirmed the noise. it seemed less noticable up to 60km but when i came towards a stop i could hear something.
my question is, being a 4x4 noob, is this normal? i`ve only put the truck in 4wd a couple times when i needed it for a short period when i had to go up a snowy driveway for example, so i`ve never noticed anything.
it has around 9000k on it, and the hubs are in auto.
thanks in advance.