Ha, I had the same type noise on my crx once. at one point I was going down the road and heard a blot fly under my car. Couldn't tell if it came from my car, or was on the road, and my tire picked it up. Well, it came from my car... My brother and I got under the car looking and tightening anything and everything but nothing seemed to be loose...untill we noticed the missing bolt in the cross member. Then noticed 2 other ones were loose. Tightened em, and noise was gone.
Scary stuff...I had gone over 130mph plenty of times with it like that...any one of those times a few more bolts could have flown out and I could have been end over end. Anyway, check out those bolts, it's a possibility. On mine, it happened everytime I accelerated, and when I started to brake. If I accel'd or braked easy enough, it wouldn't do it. Good Luck man, Nice CRX btw. Always CRX FTW