was wondering if anyone could help me

a couple of weeks ago i started to get a really bad interference sound through my front speakers

its not the engine noise its more of a crackling a loud crackling at that

now heres the strange part

it only happens when im driving and when i press my brake pedal it starts the crackling

but only does it when its on cd

radio is fine just cd

im running 3 amps, 3 set of rca 1 for each amp and it only does it through the front speakers

ive checked virtually everything and was hoping someone maybe able to help me as i havnt got a clue now