Nissan: Nissan Xterra/Frontier braking problems!

Hello!

I own a 2000 4X2 Nissan Xterra. I think I bought it when they first
came out in May of 1999. Anyway .... it's been good to me. I have
over 117000 miles on it, and no major problems except ..... When I
drive it for say 20 - 30 minutes when I brake I hear and feel a loud
vibrating noise/sensation coming from the rear/right side. The
noise/vibration usually vibrates the whole vehicle. I was told by 1
auto shop that it was the front/right side caliper. Another place
said it was the rear brakes. Well I had the place that said it was
the rear brakes replace them, and guess what .... it's still doing it.
Outside of taking it to the dealership .... does anyone have any
ideas of what I could have a repair center check? I know anyone who
has a Frontier 4X2 may have run into a similar problem because the
Xterra is built on the frontier frame. Any frontier owners feel free
to share any similar experiences you have had with me. Feel free to
e-mail me at net!

Thanks for your help,

Frankie