after having my tundra serviced(90,000miles) and the gear fluid changed in the front 4x4, now I can hear a faint grinding sound as the truck reaches 30-35 mph. its gets fainter as the speed gets faster, but the grinding sound was not there before I had the truck serviced.
can hear a noise in the l.f 4 wheel drive. on 2002 Toyota Tundra
If it happens every single time, take the truck back to shop who performed your service and take the technician on a ride with you and make him listen to it and tell you what it is. This is the best way to get help, and they should help because they performed your service last.