If you're technical this is a good read.

http://www.delphi.com/pdf/techpapers/1999-01-0142.PDF

I for one didn't understand all of it but a lot of it made sense, it's a good read and explains some of it. If you read down a bit it states that some of the squeal wasn't necessarily just the pads but the rotor contact as well and that when they changed the metal the rotor was made out of halfway through the project it shifted the frequency of the squeal.. So it may not necessarily just be the brake pad but the rotor and pad together due to the high performance braking system it could be normal simply because of the material the brakes pads are made out and the kind of contact between the rotor due to the pads having a mix of materials the stock pads have. Either way the link is a good read.