Thanks for the inputs guys. I finally found the problem. It's the rear brakes, they've been frozen for awhile. This is what they looked like...



They're rusted so bad to the point that the pad didn't make any contact to the rotors. The main reason they're rusted was the boots of the two bolts in caliper bracket were ripped. Water, salt and all kind of debris got in there and freeze up the bolts which prevent them moving in and out. Here they're



I had to cut off the old boots in order to remove the bolts. The replacement boot kit was $9.99 at any autopart stores. Put everything back together



After a quick ride, ALL the rotors are a little warm NOT the only front rotors. The car stops much better and no more vibrations.. I'm soooooo happy.

 

Glad you solve the problem :-)

 

thanks piggy