Some of those decrative pieces on the motherboard heatsink can slide off. On my S775 Foxconn x38 board I had to slide half of it off because my 212+ wouldn't fit.
It won't get hot enough to melt plastic. I agree that noise is mostly. Warping of the fan shroud so the fan blades hit is also possible if enough pressure is applied. That's one thing I like about the 212, the fans slide into position so if you need a bit more room you can just slide it up. Or see if that heatsink cover will slide off.
Bingo! A little screw takes that cover right off. Thankyou.