Okay here is a pic of a shock assembly:
At the top of the spring is the shock or spring cap. It has 2 threads on top, and a rubber bushing in the center.
Here is another view:
Most people tighten the nut in the center before reinstalling the shock. If the other 2 threads are not aligned it can be twisted until they are and still go in. This puts the bushing in a bind and it will make it squeak. It's best to align the cap before installing the shock, and also grease the bushing. I'm still not awake so let me know if you need further explanation.