What HeDog said is part of what my problem was...but I actually had the nut as far down as I could go so I just put some rubber washers under there and that fixed that.

For your "pop" what it is is that coilovers are so much shorter than springs and that means when your car is on uneven ground the piece that is on top of the springs (a little cover thing) goes up and your springs stay down and when the come back into contact with each other it usually doesn't go perfectly back in so it forces itself and when it does that you get a loud "POP".

I don't think there is anyway to solve this except for raising your car a little so that the spring and the top cover stay in contact with each other.