Where'd you buy from?
Do you know if your rifle was from someone's old stock or was it new from S&W. I've seen people speaking of this on the S&W M&P 15-22 Forum. There were 2 problems with early rifles that caused FTF / FTE. The bolt spring was switched to a blue spring and the extractor was bent to a specific new angel. If you go to the Official S&W Forum they have an M&P 15-22 page and one of the threads on it is a Serial Number Check to estimate the date of manufacture.
Not to rub it in but I am thrilled with mine -- I've shot just about every brand of ammo (bulk & match grade) and I have not had any issues to date. Pay close attention when you clean the rifle - the extractor can be bent if a patch gets snagged and you pull.
RP
Congrats. Get some spare mags while they are available: http://www.midwayusa.com/product/685791
Mine has the non-threaded barrel. It only a couple of weeks old so I sent it back to S&W on their dime. I looked for serial numbers, mine starts with DZB.