Depending on what adapter is used, some of the kits require you to grind part of the inner caliper out to create more clearance for the rotor to turn. Especially when the rotor warms up it expands a bit which can rub on the caliper. Which makes a horrid metal on metal squeel when you brake.
Pop the wheel off and look at the outside rotor edge and caliper to see if they made contact or have enough clearance.