hmm k well recently when i press my brake my stereo turns off...and then powers back on like 2 seconds later

and i noticed my voltage is going all over the place now too...like sometimes ill press the brake and it will drop to 11.2 or something and other times when im driving it goes as high as 15.4 O_o

so im wondering is it my alternator? bad ground somewhere? or is it something else?

thanks