I bought a brand new truck last week. Was all excited about the power roll down rear window. It's a 2012 (leftover), I had the 2008 model so I knew they were solid. Going home, I put the rear window down and immediately noticed *rattle rattle rattle* Metal on metal, coming from the window. Absolutely driving me out of my mind. Had the GF drive it while I sat in the back seat listening for the rattle. She started going on with the "This is a brand new truck, just take it in to service and have them fix it" And she has a point, I tell everyone that I buy new vehicles because of the warranty and I don't want to be dealing with failures on my own.
But I buy them for the catastrophic failures, tranny's, engines, axles wiring harnesses. I made a quick assessment in my head "Hour to the dealer where I bought it, up to 5 hours waiting in their shithole service department, hour home and there's a good chance they'll try to feed me that shit about it being a normal rattle or they didn't hear it." So, I rode in the back for a mile, narrowed down the sound to the tailgate, took the tailgate apart, found the metal on metal contact, tightened up the rod and voila. Problem solved in under 30 minutes. I shouldn't have had to do this, my warranty should have covered this, but frustration and time wasted waiting pisses me off.
You shouldn't have to diagnose this yourself, you could have a lemon, but from my personal experience with the 3 M&P's I currently own, the one I sold, the 2 extra slides I have and the 10+ I've worked on. I doubt you have a lemon. For $4.98 from SSS you can order the parts (Plus shipping via usps) and 20 minutes of your time with a hammer, punch and file. You can rule out what really is a very simple problem and in my experience is the only common problem with these guns. Or, you can wait till smith reopens in 14 days, spend 45 minutes on hold, pay to ship it back, most likely get 1 of the 2 problems fixed (if any, their customer service sucks) receive it back over a month later and then get frustrated again.
I like having a nice low heart rate throughout the entire day. The one time I've sent a product back to S&W and it came back with the same problem, I went through the roof with anger, it's just not worth it to me. But, to each their own.