Brake Squeal

My son-in-law has an '05 Hyundai Elantra. We changed out the front pads (semi-metallic to semi-metallic) in the Summer of 2008. We inspected the front rotors and they were in good shape and we did not turn them. All has been well up until 2 months ago when my son-in-law stated that a high-pitch squeal occurs. I have not been able to reproduce the squeal when I drive the car. Note: Rears shoes, drums and wheel cylinders are all in good shape. Yesterday, I applied some anti-squeal compound to the backs of the pads to see if it dampens the squeal.

My real question is: Are semi-metallic pads softer - and therefore less prone to squeal - than ceramic pads? I have heard that ceramic pads last longer but are more prone to squeal and wear out the rotors more quickly. Basically, I want to know if it would do any good to replace the semi-metallic pads with the ceramic pads. I don’t think so but I’m not sure. I believe that the car’s OE pads were semi-metallic.

Thanks much.