I just started to notice this on my 2006 WRX. Sometimes when I start from a stop at a stop sign for example once I give the car gas and I start moving I hear a slight pop/clunk sound from the front end. It doesn't always do this. It's very intermittent. If I stop at 10 stop signs I will probably only do it once. I have not noticed it between gears or down shifting, just starting from a stop. I can slightly feel it on the floor boards. Where should I start looking?