I checked the preload before I put them on I was thinking endlinks also. But I got to wait till I got the $$$. I also tightened everything pretty well, all though not to spec because I don't have a torque wrench. I also forgot to put I installed a spc camber kit.
I bought BC coils few months ago and about 3 weeks ago I heard a squeaky knocking sound and after reading about how coils can make noise I thought it was this. Took it to mechanic and it wound up being both my left and right cv boot gone bad. Visually looked outside no cracks but inside no grease. Just my story not sure if helps but good luck !
I told you, it's either your spring insulator, bushing or the preload. When I had springs, I had the same problem except only in the rear. I was cheap and just wrapped the top and bottom of the springs with tool box drawer liner and checked and some of the squeak was gone. Then I pulled them again and properly pre-loaded them and they were 100% quiet.
I had the same problem too when i bought my megan purple coilover. It came from the back also. My problem was im guessing it was too low (sounds weird considering thats what they are for). I had them maxed to the lowest and they squeaked for like 2 weeks staright. So i just raised it back up like 2 turns and it never came back. If u r maxed out, try raising it a hair and see if that helps.