Glad to hear i am not the only one with noises, i have had my Z for about 2 years now.
I installed 326 Power Coils probably 5 months ago and noticed immediately that when i took off i heard a clinking noise coming from the rear.
i have messed with everything i could think of and there is still a noise but now it is only when i have my car parked for a couple of hours and drive at a low speed right after starting.
After about 30 minutes i no longer hear any noise what so ever.
Unfortunately i have had a hard time finding reviews or even just people who actually have them hear in the states that i could reach out too or see their experience with them.
However they are great, best ride i have ever felt and had in a lowered car.
For me it was well worth the price!
