My friend works as an engineer for Nissan, he told me that it was a known problem with the Z's tranny. Now he could be wrong, but after listening for myself it makes sense, when the clutch is fully engaged to the flywheel there is no sound, but put it in neutral and listen to it "chatter", let out on the clutch and listen to the flywheel and clutch engage, you'll notice it resonates the sound out with the chatter getting progressively louder until the clutch is fully engaged and the chatter stops. But once again it is not a mechanical issue, the transmission is mechanically sound. It is just not ideal in aspect of audible noise. Not all dealers know what they should, in fact most dealers have no idea on anything. I had a civic that had a annoying squeak coming from the right front end, After bringing it to numerous HONDA dealers to diagnose the problem only one dealer came up with a diagnosis...he told me my aftermarket strut tower brace was rubbing on my ac line...ok i will buy that, tried it for myself, nope couldn't duplicate it, wasn't the strut brace, about month later i get a letter from honda, "defective strut" recall for my particular civic, long story short strut replaced and problem fixed. Most dealers are not as informed as they should be.