I hear a rattling sound when braking in neutral with A/C on. Is this normal ?
 

It only lasts for about 1 and a half second and the noise quickly fades. Only happen when I'm braking in neutral with the aircon on, do you guys think maybe theres a problem with the aircon ?

Perfectly normal on most cars including these. You can just hear it more on these because of the minimal soundproofing so it seems worse. Don't sweat it.

I down shift every time I slow down.....

Me too, but there is still that couple of seconds of clutch in brakes on when too slow even for first where you can get the rattle.

http://www.ft86club.com/forums/showthread.php?t=12429 watch the video i assume you have the same problem. I have this problem with my car also