Sweetred95ta

My girlfriends 97 firebird is having some problems. First off, when she drives over 50 mph and then pushes the brake pedal down the speedometer goes crazy, it jumps around untill she lets off the brake. Second, for the last couple of nights every once in a while the radio will make a popping sound and go off for a few seconds and while the radio does that all the dash board lights come on. It only last a few seconds each time it does this. What could be causing these problems? Please help!
Thanks,
Benji