so I traded today for a nice condition older M&P9..with case and (5) 17rnd mags...the date on the case is  2009... the night sights are spent.. but I have a HiViz front sight laying around  I am going to put on it, the rear doesnt bother me yet.  
my question is ... why does the recoil spring make a high pitch squeal noise when  pulling the slide back? my M&P 40 never sounded like that... I tried gun oil at first, then CLP, then grease.. nothing helps.. it is still there. the spring is not broken, and appears to be in good condition...any thoughts?

Normal.  Shoot it and hope it doesn't group like a shotgun.
(If it does shoot terribly, S&W will take it back and give you a new barrel)

that "grouping" issue is the whole reason I sold my M&P .40... 10 yards and a 6" group

Did you try shooting it rested on a bench?  Some people just shoot certain guns better than others.
I knew mine was bad when I could shoot an identical M&P40 like a laser.
When I shot my M&P 9 (1.0) from a bench it was ~4" groups at 15yd (not terrible for a defensive gun) except that there were several random fliers well outside that per mag, regardless of ammo.
I was tired of being frustrated by the steel tree in matches, I was tempted to go back to my M&P45 and give up capacity for known accuracy.  I sent the 9 back to S&W, got it back with a new barrel last week but haven't had a chance to take it out yet.

I also bought a 5" 9mm 2.0...