It's a silly thing really. During winter I get a pretty much non-stop little buzz from the rear seat. I blame cold vinyl seats and seat belt buckles.
Although I would not classify it as a problem it does irritate me a little bit, just the pitch of the sound.

Anyone is getting it too?

I think I might buy black sticky felt and place it on the buckles :)

haha this is very annoying to me too. I hear it sometimes when I am driving too, normally I have the music up or the blower on so I cant hear it but it is annoying.

But ya I think it is just the seat belts and stuff on the back bouncing when I hit a bumpy surface or stuff of that nature. But lets see if anyone else has the same problem!

I think it's one the buckle receptacles (not sure what's the correct term here :)) ... there are 2 together towards the right side. I can tap on one with my finger and it makes the very same sound. Also the location is consistent with where I am hearing it from.