Soon after my left front strut return and change-out the right started with the same noise. I finally could not take it anymore and took it back for an exchange. This was July 2015. Within a month the clunk was worse. I did a google search for "Monroe quick strut problems" and wouldn't you know it this loose nut/clunk is pretty common. I went back to the parts store and showed the guy some online threads I printed and told him the second strut I put on just a couple months ago was now clunking. He agreed to exchange it again. I put the new one on tonight and it is solid once again. No clunk/rattle. I hope it stays that way.
Buyer beware of Monroe quick struts. Maybe they have the quality/assembly issues corrected now but it took me two years and a lot of aggravation to finally be satisfied.