When ever I drive my truck I hear a hollow whirring sound that seems to be coming from the rear axle. I hear it when I back up or when going forward, it doesn't seem to change with speed.
Has anyone else experienced this?

I haven't taken it in yet for it officially (I told them about it when they repaired my shifting issue but didn't have it written down as a service complaint at the time, My service manager drove me home in my truck when I dropped the truck off and I told him about it then.)

I don't know if I'm hearing things or if its normal and I don't have any windows open when I hear the noise (Service Manager asked that as he was driving me home so apparently he heard it also )and I have the Factory tires and wheels .

Just curious