I have a 99 F250 SD 4x4 Diesel and have a loud grinding or some kind of sound comming from the front drivers side of the truck when turning to the left and sometimes sitting still with the truck in drive and my foot on the brake. I have replaced the sealed wheel bearing unit. The noise sounds like it could be comming from the brake hydro booster?? I went to a local Ford Diesel mechanic for his opinion and he agreed it sounded like the hydro booster but could not pin point the problem. Has anybody had this problem?

 

Your thread title is misleading, because it is obviously not the wheel bearing. You changed that already, and since it does it when sitting still, it is not any running gear, or 4WD lock, needle bearing, etc.

I would guess it is the power steering pump, rather than the booster. Simply because that is where the moving parts are found. A good shop should be able to pinpoint that.