Description of the noise:
- Sounds like a plastic bottle popping back into the original shape after it has pressed in.
- Noise comes from rear that sounds like clicking/tapping.
- With the rear seats down, the noise becomes sharper that sounds more like popping/ticking.
- It happens regardless of the vehicle speed.
- It happens even on a smooth road.
- It starts after some miles are put on. As early as 600 miles and as late as 3500 miles. Mine started after 1k miles.
- You may not notice the noise if you always have the radio on.
- It happens as often as 10 times in 1/4 mile, but sometimes as seldom as once every 5 minutes.
-
This is not any of the 6 noises below:
-- 1 --The rattling noise of the 3rd brake light housing.
-- 2 -- The tapping noise of the emergency trunk release cable in the trunk.
-- 3 -- The noise caused by the rear seats not fully locked in place.
-- 4 -- The rattling/buzzing noise caused by the transmitter not being snug.
LINK
-- 5 -- The rattling noise caused by the white plastic clips under the foam layer below the trunk liner. LINK
-- 6 -- The popping noise caused by the rear seats latch.
LINK
Video of the Noise:
[ame]http://http://www.youtube.com/watch?v=BNdbWnXqwps[/ame]
The sources of the noise:
Source #1
Source #2
Solution:
TSB(11/13/2012): Subaru released TSB for this noise. 12-140-12
Quick and Easy Fix:
For source #1, press the red circle in the above picture with your thumb firmly and apply a lube spray (silicon lube spray, White Lithium Grease spray, WD40, or etc.) as shown in the above picture.
No easy fix for source #2 as of now since it requires to remove the rear deck panel.
Fix done by the dealers in Japan: Adjust the spacing of the sources of the noise to stop them from rubbing. No spraying or center punching is done.
Fix done by the dealers in U.S. (Prior to TSB):Center punch the spot welds..
What to do after the noise is gone:
[Thanks 
] all my posts in this thread. j/k 
Another popping noise fix found by CJB:
Where to access the location from.
Source of the noise and the fix.
Another one by Mikepage:
DIY - Fix your Rear Deck "popping/clicking/tapping/ticking" noise.
Old news from here. Leaving them here for the record only.
8/3/2012
I just found a new information posted on a Japanese message board dated 8/4 (Japan is a day ahead of U.S.)
Description of the defect:
Below the 3rd brake light mount, there is a panel that is welded on to the body. Some cars don't have enough weld and the panel rubs against the body causing the noise. This issue is registered as a known defect at the dealers (... in Japan).
8/7/2012
Scion reference number is 1208070591, if anyone is willing to contact them.
LINK >>>>>
HERE!
8/20/2012
First FR-S in U.S. is fixed.
TAS# 122230369
LINK >>>>>
HERE!
8/23/2012
The more of us taking an action for this problem, the earlier we get our cars fixed. It only takes 5 minutes of your time to help yourself and everyone else with this problem.
Scion Contact >>>>>
LINK!
Subaru Contact >>>>>
LINK!
9/5/2012
Most likely the first BRZ fixed in U.S.
LINK >>>>>
HERE!
9/6/2012
Just the center punch seems to fix the problem.
LINK >>>>>
HERE!
9/21/2012
A one minute quick and easy fix that is to apply a silicon lube spray in two spots in the trunk behind the rear seats & below the rear deck gets rid of the noise.
LINK >>>>> HERE!
The source of the noise:
The two spots in the red circles below.
Solution:
Quick and Easy Fix (9/21/2012): Apply a silicon lube spray,White Lithium Grease spray, or etc. inside of the two spots circled in red in the above picture.
I sprayed WD-40 for three to five seconds in each hole until it started to drip and there has been no pop since 9/21/2012. *UPDATE (11/13/2012)* Subaru's TSB shows more specific locations to spray the lube.