Brake pad life is not measured in miles. There are WAY too many variables. I've seen pads last 7,000 miles on brand new Ford trucks and well over 100,000 miles on the my Grand Caravan. Neither is normal nor abnormal.
A "shimmy" is a vibration, not a noise. If you have a vibration suspect warped brake rotors. If you have a sound it could be caused by something as simple as rust buildup on the rotors or as serious as worn pads and the backing plates are starting to grind on the rotors. A brake system inspection is probably in order.