I would change the rotors you are over the wear mark. Maybe because the pads are now enclosed from the sides (they float now in a bed due to the rotor wear), it could increase the vibrations causing the squeal sound. Either use then new pads or make sure they are flat again by sanding them.
I have had good experience with the Hawk ceramic ones when it comes to no squeal. Just make sure you do the brake job properly as fmertz says don't be shy with grease.

 

I too had a nasty 'squeal' on my discs. After my local garage took a look it was soon fixed. This is a note at the time the job was done. May give you an alternative idea of what could be wrong. Dust shields? Have a read Click Me To Read


Good luck!