on the e34?
1 Is it only when stopping under brakes?
2 Did you replace the rotors? Whish kind?
3 Did you bed them in?
If yes to the above, they may still be glazed- you have to inspect them. Could also be a loose pad/s/locator spring/s.
I use new rotors and pads every time- and use Akebono ceramics, costly, but no probs ever. One day when my brakes again save my/someone else's life, I'll be glad about that