I bought the used D2 coilovers off of here for my 2010 G37x sedan. I've since completely torn them down, replaced the rear shocks, gave them a thorough cleaning, lubed them and reassembled them. They've been on the car for about 2 months now. I was having some thunking issues from the front, but turns out that was due to some major shoddy alignment work by a local shop that didn't tighten half the suspension on the front. The thunking turned out to be the multi-piece ball joints of the Z1 control arms that weren't tightened down all the way.

Now that I've got all the major noises fixed and some time on the coilovers I am getting a slight creak from the front coilovers. It only happens when I get full or close to full extension of the front suspension. I never or very rarely hear the creaking on the highway unless I hit a pretty good size bump in the road or crack.

Anyone have any recommendations on where to look first? I've had the front wheels off a good 5 times trying to track down this noise. Everything is now 100% tight and secured.

Overall I'm very happy with the coilovers save for the slight over-stiffness of the springs.

Edit: Pic in this link for reference. The bodies of the coilovers in this link are the same as what I have:

http://www.ebay.com/itm/D2-RACING-RS-36WAY-ADJUSTABLE-COILOVERS-SUPENSION-Infinite-G35-SEDAN-03-04-07-/262130766705?fits=Model%3AG35

 

Sounds like it could be coil bind, google coil bind and you should get some good info. I think that's what I have w/ my COs, it's only when I go up a steep incline at an angle (my driveway for example), where the front tire is almost fully decompressed as the load shifts to the rear opposite corner. Other than that they're pretty quiet.