This is the 2nd hertz work truck i had doing the same thing they are both 2004 F150 sc 4x4 with the 5.4 and manual shift lever for 4wd.
It sounds like it is coming from the left side on the front axle, and i tried the 4wd today because i had it stuck in some mud and the 4wd doesnt engage the front axle.Now the grinding noise seems louder than ever and wont go away i tried re-engaging, backing up and even tried 4wd low and grinding is still there.
Tommorow morning i will drive it 90 miles to work, there is no hazard to driving with this noise is there? I mean it wont lock up will it?