This just started happening recently, but I noticed when I'm going on/off the throttle at low rpms (regardless of whether I'm shifting gears or not) there is a small *click* sound. I can't really tell which end of the car it's coming from, but it happens pretty consistently and doesn't seem to go away once the car is warmed up. I tried searching on the forums briefly but couldn't find much. Some people said to re-tighten the rear axle nut. For what it's worth, a couple weeks ago I self-installed an Invidia Q300 dual exhaust. That involved unscrewing the 3 bolts at the back of the cat to remove the OEM exhaust, but I'm pretty sure I tightened those sufficiently.

If needed I can try and record a short sound clip of it later.

 

check the torque on your axle nuts.