shift grind?

I figure it's about time I ask about this. Since back in early winter I've been noticing this in my truck. When taking off and leaving my driveway and getting on the road, the very first shift after sitting overnight from 1st to 2nd gives off a kinda grinding noise, similiar to the noise you get when spinning your tires or the ABS. I only notice it on first to second shifts, and its usually only in the morning after sitting over night. Dealership couldnt replicate anything last time I took it in. Anybody know what it is?