Noises when steering right or left only under vehicle load and only when it's been driven a little while?

My 2003 Mazda 6 is making a grinding crunchy noise coming from the front of the car when turning the steering wheel right or left and it doesn't have to be turned far at all to make the noise. It only does it under vehicle load and it only does it after I've been driving it for a little while. We have replaced the struts & upper control arms with bushings on both right & left front. The noise is still there. At this point I'm in for $500 and next week will be in another $200 to next replace all 4 lower arm controls with bushings, front brake pads (50%), and tie rod ends on both left & right front. I can't keep playing these guessing games with the mechanic about what it COULD be, I can't afford to replace everything. Any body have any ideas as to what my problem is?