What sound could this be?
 

On Saturday, my BRZ developed a rattling noise. I first thought it was from the rear deck but now I believe it may be from the driver-side rear wheel well.

https://www.youtube.com/watch?v=ob7x...ature=youtu.be

https://www.youtube.com/watch?v=bdEq...ature=youtu.be

These are my observations:
--This noise is only present after the car has been running for at least 25-30 minutes
--Once it begins, it is occurs in any gear, at virtually any speed above 10 MPH, and does no matter whether I am in neutral or not, or whether or not the clutch is depressed
--The sound changes when going over bumps
--The sound appears amplified when making both right and left turns, but especially right-hand turns
--The sound changes in pitch and slows in intensity/frequency as the car slows (see video)
--The rattle was present on both Saturday and Sunday – it may be coincidence, but both of these days the outside temperature was about 65 F, and this is the warmest the outside temp has reached during the time I have owned the car

Unless I am missing something really obvious (which is completely possible), presumably this will mean a trip to the dealer, but having some idea of what it is beforehand (from both a time perspective for repairs and knowing it is OK to drive to the place of service) is always a plus. Could this potentially be a pebble lodged between the disk rotor and the metal guard behind it? Many thanks!

My best guess is that the rattle is coming from the rear package shelf...area where the third brake light is.

Best way to get help is to find another person willing to lie in the back with the rear seat back down... Listening for the sound, then putting hands on where sound seems to be emanating from.

Dealership will put their least experienced person on the job...someone they don't pay much. This sometimes gets the problem figured out, often though not.

Rattles in package shelf area were very common on 2013 early production models. I don't know just what all the fixes were.

I have a 2015 FRS, no problem until recently, at over 50k miles on my car. My car rattles from package shelf area at 70 mph and then only sometimes. Wiggling the plastic cover for third brake light sometimes makes the sound go away yet not a permanent fix.

Best to have a friend who is good at being patient, working with you to find a fix.

Some package shelf rattle fixes within this Google search:

https://www.google.com/search?q=ft86...hrome&ie=UTF-8

That would make sense - no issues were found, dealer could not reproduce it (which figures as today was colder than the day it appeared and after - and it seems like such things happen only depending upon temp, which I assume is related to all that expansion/contraction science) - so it sounds like I may be Dynamatting the rear deck...