Wa wa wa wa as I'm braking

I have a 1995 Mazda Truck, B2300 series that is a 4 wheel drive. Recently I had the front brakes replaced, new clay disc brakes. Not so long after that I started to hear a noise as I was braking as well as squeaking. I thought, of course it had something to do with the new brakes. The sound happened occasionally at first and now is every time I brake. I can hear it as I’m coming to a stop, sounding like it’s coming from the rear. It’s a rubbing type noise, like a wa, wa, wa, wa that happens until I have stopped. After 2 mechanics I now have a $700 estimate to replace the u-joint, and they aren’t even sure if that will fix it. The front brakes are new. The rear drums have been replaced and machined to fit properly (they thought that was the issue). Anyone have any experience with this? Is this common or something that I have to fix every such and such miles? Thx -Christine

Go to a secluded parking lot and use the parking brake to stop several times and post back the results here.