What makes a grinding noise on a ford expedition when giving gas?

It could be a couple different things. Most obvious would be brakes. If a brake is sticking and worn you could be hearing a grinding noise as you accelerate. Second could be a driveline issue. Worn u-joints or something sticking in the transfercase (4X4) could also cause a grinding noise. Best advise is to find a reputable service shop and have them diagnose the noise properly. Good luck!