It may be a simple alignment issue. I used to experience squealing brakes until I learned to re-align the calipers to the rotors. I now make this adjustment regularly. It is not hard to do.

The directions can be found here.....

Avid BB5 User Manual

In brief, the steps are......

ALIGN THE CALI PER
A. Use your fingers or a Torx® wrench to turn the inboard pad adjustment knob
clockwise until the rotor is centered in the caliper. This positions the pads for
the next step in the installation.
B. Make sure the CPS bolts are loose enough for the caliper to move freely.
C. Squeeze the brake lever to compress the brake pads firmly on the rotor.
D. While still holding the brake lever, tighten the CPS bolts. Once they are tight you can
let go of the lever.
ADJUST THE PADS
Back the adjustment knob off (counterclockwise) until the rotor spins freely.
Now you can dial the pad in or out until you find the brake action you prefer
(make sure, of course, that there’s no drag on the rotor). If you can’t seem to
get the feel you like, or the rotor is dragging, repeat step 5.