I have a 1999 Ranger XLT 4.0l 4X4 Extended Cab. I have an intermittent nasty grinding noise coming from the right front end that only happens once out of every 5 or 6 times I use the truck. This sounds like metal on metal grinding but everything appears to be ok. I have already replaced the brake pads, calipers, rotors, and hubs. I’m at a loss of what to do next. Any advice would be greatly appreciated.
I forgot to mention a very important piece to the puzzle, it only makes this grinding noise while I'm braking. I also replace the upper control arm.
Sorry for forgetting that very important piece of info,

 

Checked your CV axle boots for tears?

 

The CV axle boots appear to be fine.

 

Test your 4WD, see if it is working.

'98-'00 used PVH auto hubs which were problems as they aged
Good read here: Permanently Lock Your 1998-2000 Ford Ranger PVH Pulse Vacuum Hubs

For the wheel bearings read here: TRS Magazine - 98-00 Ranger Hub/Bearing Assembly Replacement

 

the 4 wheel drive is working although it is clunking into 4 wheel low

 

The 4 wheel drive is not working properly, it is going into 4X4 but it was not coming out ok. I had a crack in both hoses. I replaced the hoses and now the 4x4 is working properly. Could the leak in the vacuum line be the cause of the intermittent grinding noise? I guess I'll just have to wait and see.