Service department fixed the noise. Said they " Tightened and siliconed all fasteners above headliner and road tested the vehicle". I wonder if this information will be made available to other service departments that will likely see this problem?

so i have the base Z with the sport package, no xm antenna on the roof and this sound is about a constant on a rough road. i don't have the bose system and i just turn up the radio most times but this is annoying me. i'll tear the rear down this weekend and see if i can pinpoint it for the non-touring package folks.

Any update? I have the Base + Sport, non-Bose model, buzz/plastic rattle like you.

[QUOTE=AtlantaDave;606387]Any update? I have the Base + Sport, non-Bose model, buzz/plastic rattle like you.[/QUO

all z cars have wire antenna laid out across over your head liner. when you take out the head liner(be gentle) you will see the green color wire and that is the culprit. you need to secured the wire. do not use duck tape b/c it will not work. maybe glue or soft pads.

I FINALLY found the exact location of this buzzing noise. I had tried everything from trying to fasten all the wires in the headliner, cushioning the plastic around the rear hatch, and going to two different dealerships to have it looked at, both of which completely ignored what I said about it coming from WITHIN the headliner.

The noise would stop every time I would push up on the headliner so I knew for a fact it was either the headliner itself or something inside. I could also replicate the noise when I tapped on the rear hatch glass. I took the headliner apart probably 8 or 9 times from the back just like in Schrute's journal and looked inside. It wasn't until I closed the hatch while in the trunk with the headliner open and my arm inside. I would blindly hold things inside the headliner and with my other hand tap on the glass to see if I could hear the noise. Doing this I finally figured out exactly where the noise was coming from...There are two metallic canister/capacitor looking things (anyone know what these are for?) right at the crease where the roof bends upwards, one on the drivers side, and one on the passengers. The one on the passengers side seemed to be loose and it was rattling against its own hinges. I just secured it as tightly as I could to the roof with double sided tape, not the cleanest thing but I haven't heard the noise in months! I seriously lost sleep over this and I'm glad it's over with. If the noise comes back It'll be because the double sided tape broke or came loose, at that point I'll take it to the dealer and tell them exactly what it is and have them fix it.

Hope this helps all those who still have to deal with this.

It being metallic also explained why I could hear it in the morning or when the car was cold but it would go away after 20-30 minutes. The metal was expanding as the car got hotter and it would tighten it up against the hinges stopping the rattle.

Buzzing Noise from Rear Area
 

Funny follow up to my original post. I had this horrible buzzing noise in the rear headliner since I got my 370z in late 2009. About a month ago I was driving with my wife at night and ran over an abandoned tire (with the wheel in it) going about 60 miles an hour. This destroyed both right tires and wheels. Cost to fix was about $3,000 but insurance covered most of it. Good news in all of this is that the trauma of the collision must have knocked whatever was loose in the headliner back where it was supposed to be. No buzzing noise since the accident.

i have a loud humming noise too when i left off the gas after WOT 4k+ RPM.