Over the last month or so, I've noticed I get a loud rubbing or groaning noise from the rear end of my truck when I back up in reverse. It is really loud when I first back up, but after I back up a couple of times or continue backing in reverse for a little while the noise goes away. If I use reverse later on in the day, the noise isn't there. It seems it only happens after the truck has been sitting overnight. Temperatures have been fluctuating from about -5 degrees to about 30 degrees over that time and to me it appears the noise is more prevalent on mornings when it is warmer outside. I did take it to the dealership to have them look it over because they thought it might have something to do with the slip yoke. They checked that and it was lubed good enough so they said that wasn't the problem. The technician advised that it looked like the e-brake pads were possibly binding causing them to stick to the rotors. They wanted $400 to repair, so I said no thanks and took it to my local mechanic. He looked at and said he couldn't really see nothing wrong with the e-brake but I told him to change the e brake pads and springs anyway since he was already looking at it and he also replace front pads and rotors which fixed my front end shimmy. Anyway, the noise is still there even after replace the e-brake components. Anybody have any ideas of what it could be??? Thanks.