I have an N15 pulsar that has a R32 GTR front brake upgrade fitted (non-vspec sumitumo 4-piston calipers).
Not using adapter plates, using an N16 knuckle which the caliper bolts straight onto.
The brakes scream like a banshee sometimes (F**KING LOUD!!), when they're cold they do it, when they're hot they do it... sometimes they shut up and then it comes back again, usually only happens on light braking (like normal driving)
Discs are DBA4000 slotted items, which have done quite a bit of track work, used ferodo ds3000 pads on the track
I've tried the 3000's on the street, tried lucas pads, bendix ultimates, and am now using standard nissan pads (200sx factory pads) and they still scream like a bitch under light braking. I've put in the nissan factory shims behind the pads which has that orange goo as well, hasn't helped. Still has the caliper pins and the retaining springy bit that pushes down on the pads. Have even rebuilt the calipers with a genuine nissan kit, didn't help.
I'm thinking that maybe cause the discs have copped a lot of abuse on the track the heat cycles may have affected them somehow?