Whenever I go in reverse and start backing up..it sounds like my suspension is binding (it's a popping noise). It doesn't do it going forward though, only reverse.
I have sub-frames, upr spherical upper and lowers, eibach sportlines, and stock sway bar.
I noticed a slight popping noise too when backing-up after I swapped all my rear control arms. But I did notice that the sleeves in the chassis bushings on the FMS uppers do not fit snugly on the bolt (there are little round stubby things inside it that sort of make contact with the bolt). I'm assuming its supposed to be that way, and I compared them with the stock arms and they were the same. I'm assuming that the sound comes from the axle shifting towards the front of the car when you back-up and the bolts hit the other side of the bushings. I not really sure, but I only had a glance and none of the bolts backed-out or anything. So I'll leave it unless it gets worse.
Also, the old rubber bushings were completely shot, so they had alot more "give", maybe thats why i didn't hear a pop with the old UCA's...
There are 3.73s in the car (previous owner had them done). It's been doing this ever since I've had the car so apparently it's not hurting anything..just annoying at times.