[jonh]

I replaced the front pads and get a harmonic noise from the right front after the car has been driven for 20 minutes. Stepping on the brake will stop the noise.
The noise will get louder at different speeds. Any ideas?

Thanks,
Jon

 

[Enganeer]

How freely did the caliper move on the slides? You could have sticking caliper with a slightly warped rotor. Running ceramic or metallic brake pad makes more noise than softer organic pads.

My trailblazer did the same thing, cleaned and greased the slide on my right front caliper (was stuck) it was much more quieter after that.

 

[Andy's Auto Repair]

Did you do the rotors? 'Cause Germanic tendencies says do the rotors.

 

[71350SS]

A metallic sqeal will usually be one of the wear sensors touching the rotors and will usually go away when you step on the brakes.If you only changed the fronts jack up the wheels one at a time after the noise starts, spinning the wheels should reveal where the noise is coming from.Its possible the rears are worn out too.If you changed all the pads inspect the clips that hold the pads in place in the "caliper bridge".
Andy's advice is also true,if your rotors had any kind of wear ridge that could be the noise too.