I purchased a Giant Escape 1 early this summer. It has aluminum linear pull brakes. Recently on a very steep decline, I applied the brakes and the front wheel started to vibrate tremendously, almost jumping up and down. I took it to my LBS they fixed it under warranty and replaced the front brakes with a different type. They said they were having some troubles with the Giant brakes. The problem went away for a while, but has now returned, although not as severe as before. I wondering if it could be poor quality pads. The rim is in good shape. I have put about 650 miles on this bike. Any thoughts?