i'm experience a similar problem here. After installing my megan racing coilover, there was a metal cranking noise. First, I thought something was loose and after re-intstalling to correct the mistake, the noise is yet gone. I'm very frustrated and I don't know if I should go with another brand or just deal with reality that coilover isn't meant to be here. Again, I don't know what causes this. I don't know if changing from a coilover to a spring would help? So guys feel free to leave me some tips or comments.

does the noise happen on bumps?

on bumps or on bumpy road surface. It's very sensitive.

im sooo glad this thread was created haha.. i just installed my BCs the other day and my car is making that same rattle..clunk.. bump.. etc.. in the passenger rear, i TOATALLY agree that noise bugs the hell out of me.. first thing i thought was somethings not torqued down all the way. but i checked and double checked all of that and now i can go back and look at all the things posted here and probably solve the problem in one far swoop :) im sorry this was such a huge situation for you to have to deal with. But im glad you got it figured out and i hope i can do the same... Thanks for all the imput, everybody! I love this forum :)

Maybe upper ball joint? Throw some grease on there, u might be changing the angle of the ball joint-upper control arm angle?