High pitch noise from right rear

Hi, I have a 2000 GT Convertible. There's a high pitch noise coming from the right rear tire area. It doesn't seem to happen until the cars been driven and gets warmed up. Once it starts it kicks in just as I pass about 30 mph and it stays constant, no sound or frequency change all the way up to fast highway speeds. It stops when I get below 10 mph. It's a high enough frequency that my friend that was helping me who's a bit older can't hear the sound. It's extremely annoying and I don't know if I'm hurting anything.
I thought it was the warning plate on the rear brakes and the brakes were almost completely gone so I replaced them (pads, calipers and turned rotors). The sound is still there. One mechanic suggested it could be the emergency brake pads, and another said that this year and model didn't have that kind of setup??
Any ideas?
Thanks
 
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