check the tension rod bushings. if they're blown so bad that it clunks whenthe weight shifts onto the front, replace immediately. if the noise is coming from the rear, disregard.
as to the strut insulator...buy them from nissan, pretty sure you can get the nismo ones.
http://www.courtesyparts.com/ ....html
thats just some random dealership in texas, your local one can probably order them relatively quickly compared to a "shop", just be prepared for dealer prices...
Micah