Squealing is usually the result of grease on the pads or rotors. No, really !
Take the pads out and sand them again. While the pads are out, clean the rotors with degreaser (or vinegar, it's just as good and a lot cheaper).
Don't forget that after cleaning and sanding, the brakes will need the usual bedding-in routine (either prolonged riding with the brakes applied or 30-ish successive stops from 20-ish MPH) before they start working properly.
However sometimes it's just the nature of that particular brake setup, and no amount of cleaning will help.
In that case, I suggest filing off the leading and trailing edges of the pads at a 45° angle. (these
aren't bike pads, but they should give you an idea)
I used to do that on my motorcycles and mopeds, and it was a sure way to stop any squealing. Worked on my Bulls' original Formula brakes too.
Don't worry about the (small) amount of contact surface you'll lose, you'll have plenty of braking power left.
It doesn't hurt to do everything at once. File off the edges, sand the braking surface and clean the rotors.
EDIT : Considering you changed the rotors, it just might be that the pads and new rotors are a combination that's more likely to squeal.
I think I have the same rotors (Hope Saw, right?) on my Bulls, and they're silent in combination with whatever pads came with my Formula RX20 brakes.
Still, filing off the edges will probably solve it in your case.