Ford Repair: Grinding noise while backing up, ford f 150, power steering fluid

Question
I have a 2000 Ford F-150 5.4L (7700). Recently I had my brakes redone, new rotors/pads on the front and the inspection on the rears were fine.  Ever sense then when ever I am backing out of a parking space, drive way or taking a turn about under an interstate, it feels like my truck is going to fall apart.  It sounds like grinding, but it feels like the brakes are sticking.  I took it back to the place that did the repair, and was assured it's not the brakes, and was told that it was air trapped in my rack and pinion, I'm not crazy, but that sounds nuts. Although the problem only occurs while I'm turning, which makes me think that it might have something to do with steering/ suspension. I Also was told this was common in Ford Trucks, although all I've owned is ford trucks, and this is a first for me.  So any help would be much appreciated.  

Thanks in advance

Trent

Answer
Trent, when the brake job was done they probably moved the steering while the engine was off - normal operation to move the wheels for accessing the pads on each side (happens frequently on stalled vehicle that has to be pushed off the road or into a shop).  This will cause the power steering fluid to be displaced from the steering rack and forces up into the reservoir, possibly over-flowing the reservoir, allowing air to enter the p/s lines and pump.  No harm done...
Check the p/s fluid level with the engine off, and top it off if it is low... then crank the engine and turn the steering wheel all the way to each side a few times - this will force the fluid into the rack and lines at full pressure... then turn off the engine and check the fluid again.  If it still makes the noises, let it sit for a few hours and repeat the procedure.  The air should be purged after a few of these, but if not, take it back to the shop and ask them to vacuum the p/s system to remove trapped air.
Hope this helps... and Happy New Year!
Clay