well i guess it could be a number of things but the basic thing that ive seen ths problem is lack of lubrication somewhere. my susp has been squeaking for a while now, more so when i first upgraded than at the present time. i took my car to the mechanic for it to be checked and he said its the spring "coiling" around where it seats on the strut. although its not SUPPOSED to do this i guess its just a fault in the manufactuing of the product. he said best thing to do would be to get some hard grease and lay it down on the strut seat. it helped out alot, didnt cure the problem, but its not nearly as loud.
When you talk about bushings you mean the lower ones where the strut bolts on right? i have a really bad squeaking after my coil install, replaced the struts now and its still there on the rear left strut, its really loud and annoying, sounds to loud to be comming from outside the car, its more like the sound is comming from the strut mount area in the trunk.. any ideas?
For the front camber kit people, it's the bushings. I don't know if the directions say this or not, but you have to really take apart the kit and grease every spot on the bushing. Hammer out the metal tube and everything. Even then it feels like it's a matter of time before it starts squeaking again.
Personally it doesn't bother me enough to want to rip apart my suspension just to grease it up.