Yooper,
As the others have already explained that's the e brake making that noise and it will shut off at idle once warmed up.
Interestingly though when I drive on the highway, my mileage never seems to go over 18 or so on the overhead with the e brake on, so I turn it off when I go anywhere far. Then it will go up to 20 or 21. Hand calculated I still haven't gotten much better than 19 on the highway.
While on the subject of warming up, on the highway when cold, I'll sometimes just keep the truck in fourth gear until the temp gauge hits 200 and then I'll shift it into fifth and then sixth. It seems to decrease my regens, and also keep my mileage up. I know it sounds a bit weird, but it seems to do the trick.
The times I just hit the highway cold, my overhead sometimes drops down to about 13 or so.
I've got 26,000 on it so far and I'm still trying to figure it out.
Be careful,
John